If you're craving the ultimate indulgence, these Buttery Roast Beef Sliders with Caramelized Onions Recipe are exactly what you need. Think tender roast beef stacked with melty cheese, sweet caramelized onions, and a luscious garlic aioli—all nestled in soft, buttery slider buns. Trust me, once you make these, your gatherings or cozy nights in will never be the same!

Two toasted sandwich buns with a golden brown color and sprinkled with sesame seeds and seasoning sit stacked on a dark wooden board. The bottom bun holds a layer of melted cheese that drapes over the edges, topped with caramelized onions and slices of cooked meat peeking out from under the cheese. The top bun rests slightly off-center on the filling, showing more melted cheese and caramelized onions oozing from the sides. The background is dark, and the board contrasts with the textures of soft buns, shiny melted cheese, and juicy meat and onions. Photo taken with an iphone --ar 2:3 --v 7

Jump to:

Why You'll Love This Recipe
Ingredients & Why They Work
Make It Your Way
Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe
Top Tip
How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe
Make Ahead and Storage
Frequently Asked Questions:
Final Thoughts
Buttery Roast Beef Sliders with Caramelized Onions Recipe

Why You'll Love This Recipe

I can’t get enough of these sliders—the blend of savory roast beef and sweet onions, with garlicky, buttery rolls, just hits all the right spots. They’re perfect for when you want something special without a mountain of effort.

Next-level flavor: Caramelized onions add a sweet, jammy depth that pairs amazingly with roast beef.
Homemade touches: Garlic aioli and garlic butter sauce bring a rich, garlicky kick that store-bought spreads just can’t match.
Perfect for any occasion: Make a batch for game day, parties, or an indulgent weeknight treat.
Easy to customize: Use your favorite melty cheese and slider buns to put your own spin on this classic.

Ingredients & Why They Work

Before heading to the kitchen, let’s chat about the star ingredients. Picking quality roast beef and fresh slider buns (Hawaiian rolls are my personal favorite!) really makes a difference. And don’t underestimate the power of homemade caramelized onions and aioli—they add layers of flavor that turn ordinary sliders into something extraordinary.

Flat lay of a stack of 3 large yellow onions, thinly sliced; a small white ceramic bowl with a smooth pale yellow egg yolk; a single whole garlic clove, white and firm; a small white ceramic bowl filled with light golden olive oil; a small white ceramic bowl with bright yellow fresh lemon juice; a pat of unsalted butter, pale creamy and rectangular; a small white ceramic bowl of brown sugar; a small white ceramic bowl of coarse kosher salt; a small white ceramic bowl of deep brown beef broth; a small white ceramic bowl of dark Worcestershire sauce; a handful of thinly sliced deli roast beef, deep red with marbled fat; twelve soft, round slider buns with a glossy golden-brown crust sliced in half; twelve smooth, pale provolone cheese slices; a small white ceramic bowl of shredded white mozzarella cheese; a small white ceramic bowl with poppy seeds; a small white ceramic bowl with white sesame seeds; a small white ceramic bowl with dried minced onion; a small white ceramic bowl with garlic powder; a few whole brown eggs with clean shells arranged symmetrically nearby, placed on a clean white marble surface, soft natural light, photo taken with an iPhone, professional food photography style, fresh ingredients, white ceramic bowls, no bottles, no duplicates, no utensils, no packaging --ar 2:3 --v 7 --p m7354615311229779997

Unsalted butter: Essential for caramelizing onions and making the garlic butter sauce, giving everything a rich, creamy foundation.
Olive oil: Used with butter to cook onions evenly without burning.
Yellow onions: Thinly sliced for slow caramelization, creating that sweet, deep flavor.
Kosher salt: Helps draw out moisture from onions and seasons the aioli and butter sauce perfectly.
Brown sugar: A small touch to speed up and enhance onion caramelization.
Beef broth: For deglazing the pan with onions and building the au jus sauce.
Egg yolk: The base for homemade garlic aioli, creating a creamy, luscious spread.
Dijon mustard: Adds tang and depth to the aioli.
Garlic: Fresh garlic in the aioli and garlic butter sauce infuses irresistible flavor.
Fresh lemon juice: Brightens and balances the aioli.
Light olive oil or neutral oil: To keep the aioli silky without overpowering flavors.
Better than Bouillon Beef Base: Boosts the richness of the au jus sauce.
Worcestershire sauce: Adds umami and complexity to both the au jus and garlic butter sauce.
Slider buns: Hawaiian rolls are ideal for that soft, slightly sweet bite, but any soft slider bun works great.
Deli roast beef: Thinly sliced for easy layering and balanced flavor.
Melty cheese: Provolone, Swiss, or muenster melts beautifully over the beef.
Shredded mozzarella cheese: Adds gooey meltiness to the mix.
Poppy seeds and white sesame seeds: Give the garlic butter sauce a subtle crunch and nutty note.
Garlic powder and dried minced onion: Boost the garlic butter sauce’s savory punch.
Freshly cracked black pepper: Adds just the right amount of heat and complexity.

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Note: You'll find the complete list of ingredients, along with their exact measurements, in the printable recipe card at the bottom of this post.

Make It Your Way

One of the best things about this Buttery Roast Beef Sliders with Caramelized Onions Recipe is how easy it is to customize. Whether you want to lighten it up or add a little extra zing, there are plenty of ways to make these sliders your own.

Cheese Swap: I’ve tried using sharp cheddar instead of provolone or Swiss, which adds a nice tangy kick and pairs beautifully with the sweet onions and savory beef.
Make It Spicy: Add a few dashes of hot sauce to the garlic aioli or toss some sliced jalapeños on top before baking for those who love a little heat.
Vegetarian Twist: Skip the roast beef and load up on caramelized mushrooms and roasted red peppers; it’s equally decadent with melty cheese and garlic butter sauce.
Quick Fix: When I’m short on time, I simply use mayo mixed with a bit of garlic and mustard instead of homemade aioli, and skip the caramelized onions. The flavors still shine through, and the sliders come together in about 30 minutes!

Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe

A close-up shows a woman's hand holding a sandwich with three layers: a toasted, sesame and poppy seed covered top bun in golden brown with a shiny glaze; inside there are layers of caramelized onions in dark brown with a glossy texture, melted cheese dripping in light yellow, and thin slices of cooked meat in pink with browned edges; below is the bottom bun matching the top in texture and color. The sandwich is being dipped into a white bowl filled with thick, brown dipping sauce that is dripping down the sides and splashing on the wooden surface below. In the background, there are more stacked sandwiches with the same layers on a wooden board, set against a white marbled textured surface. Photo taken with an iphone --ar 2:3 --v 7

Step 1: Slowly Caramelize Those Onions

I start by melting butter and olive oil in a large skillet over medium-low heat — this gentle heat is key. Then I add thinly sliced yellow onions, sprinkle on kosher salt and a teaspoon of brown sugar to help them caramelize beautifully. Patience is everything here; stirring every few minutes for about 45 minutes results in soft, jammy onions that are deep golden brown. A quick splash of beef broth at the end deglazes the pan and pumps up the savory flavor. The smell alone is amazing and sets the stage for everything that follows!

Step 2: Whip Up That Creamy Garlic Aioli

To make the rich homemade garlic aioli, I whisk together an egg yolk, Dijon mustard, freshly grated garlic, and lemon juice until smooth. Then I slowly drizzle in light olive or neutral oil while whisking vigorously or using an immersion blender to emulsify it into a luscious, creamy sauce. A pinch of kosher salt finishes it off. If time is tight, I sometimes opt for a quick mayo blend seasoned with the same flavors—still delicious, just faster!

Step 3: Simmer the Au Jus Sauce

I melt butter in a medium saucepan on medium heat, then stir in Better than Bouillon Beef Base, beef broth, and Worcestershire sauce. Letting it gently simmer for 20 minutes reduces it by half, intensifying the rich beef flavor perfect for dipping those sliders. It thickens slightly and darkens—keep it warm so it’s ready to serve alongside your sliders.

Step 4: Toast the Bottom Buns Just Right

Preheating the oven to 350°F, I slice the slider buns horizontally but keep them connected so assembling is easy. Placing the bottom halves on a parchment-lined baking sheet, I brush them lightly with melted butter or garlic aioli and toast for 5 minutes until they turn just golden. This step gives the buns a subtle crispness that holds up beautifully under all those savory toppings.

Step 5: Assemble Your Sliders Layer by Layer

Next, I spread a generous layer of the garlic aioli over the toasted bottoms. Then, it’s time for the roast beef—piled 2 to 3 layers thick for that hearty bite. I layer on slices of melty cheese like provolone or Swiss, followed by a sprinkle of shredded mozzarella for extra ooey-gooey goodness. Finally, I spoon over those luscious caramelized onions evenly across each slider, ensuring every bite is packed with flavor.

Step 6: Brush On Garlic Butter and Bake to Perfection

For the top buns, I mix melted butter with Worcestershire sauce, poppy seeds, white sesame seeds, garlic powder, dried minced onion, kosher salt, and freshly cracked black pepper. Brushing this fragrant garlic butter sauce on the rolls gives that beautiful golden finish and adds layers of flavor. I cover the sliders loosely with foil and bake them for 10 minutes, then remove the foil and bake for another 10 minutes until the tops are golden brown and the cheese is perfectly melted.

Step 7: Slice, Serve, and Dip!

Once out of the oven, I slice right between the rolls to separate the sliders. Serve them warm with individual bowls of the rich au jus for dipping—trust me, it takes these sliders to the next level. Each bite is a harmonious mix of buttery, savory, sweet, and melty magic. Perfect for sharing or savoring solo!

Top Tip

Mastering these Buttery Roast Beef Sliders with Caramelized Onions Recipe truly comes down to a few key tricks that bring out all the flavors and textures perfectly. Here’s what I’ve learned along the way that makes the magic happen every time.

Low and Slow Caramelization: Cooking the onions over medium-low heat for 45 minutes is worth every second. It transforms their sweetness and softness, making all the difference in flavor.
Homemade Aioli vs. Mayo: I tried using just mayo for ease, but the homemade garlic aioli adds a fresh zing that lifts the whole sandwich to another level.
Don’t Skip Buttering the Buns: Brushing the slider tops with that garlic butter sauce loaded with Worcestershire, poppy seeds, and sesame seeds creates a golden, savory crust that’s irresistible.
Simmer the Au Jus Well: Letting the au jus reduce for a full 20 minutes concentrates the beefy flavor so your dipping sauce isn’t just warm broth—it’s rich, hearty perfection.

How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe

The image shows five pieces of bread spread with a creamy white mixture that has small green flecks, all placed neatly in a baking tray. The bread pieces vary in size and shape, with three longer slices arranged horizontally on the top and middle, and two smaller slices on the lower right side. The creamy spread is unevenly applied, with some areas thicker and others thinner, showing a rough texture on the bread underneath. The baking tray has a light beige tone, and the background surface has been changed to a white marbled texture. Photo taken with an iphone --ar 2:3 --v 7

Garnishes

To elevate these sliders, try adding fresh arugula or baby spinach leaves for a peppery crunch. A sprinkle of finely chopped fresh parsley or thyme can brighten up each bite. For a touch of tang, a few thin slices of pickled jalapeños or pickled red onions add a delightful zing that complements the rich beef and sweet onions.

Side Dishes

Serve your sliders alongside crispy oven-baked fries or sweet potato wedges for a classic combo. A crunchy dill pickle spear balances the richness beautifully. For a lighter option, a simple mixed green salad dressed with lemon vinaigrette or a tangy coleslaw adds freshness without overpowering. Don’t forget a side of extra au jus for dunking and soaking up every bit of buttery goodness.

Make Ahead and Storage

Storing Leftovers

Once assembled (but before adding the caramelized onions and garlic butter sauce), you can make these sliders up to two days ahead. Keep them covered tightly in an airtight container or baking dish in the fridge to preserve freshness and prevent sogginess.

Freezing

While freezing fully assembled sliders isn’t ideal because of the caramelized onions and garlic butter topping, you can freeze the basic components—like the deli roast beef and cheese slices separately. Thaw fully in the fridge before assembling and baking for best results. For a quicker option, prepare sliders without onions and butter sauce, freeze them wrapped tightly, and add fresh toppings after thawing and before baking.

Reheating

To enjoy your leftovers without losing that fresh-from-the-oven magic, reheat your sliders in a preheated oven at 375°F for about 10 minutes. This keeps the buns from getting soggy, melts the cheese nicely, and warms everything through. Serve again with warm au jus for dipping to revive that indulgent flavor experience.

Frequently Asked Questions:

Can I make the caramelized onions ahead of time?

Absolutely! Caramelized onions can be made up to 3 days in advance and stored in the fridge. Just gently rewarm before assembling your sliders to maintain that rich, jammy texture.

What cheese works best in these sliders?

Melty cheeses like provolone, Swiss, or muenster are perfect here because they melt smoothly and complement the beef’s savory flavor. The extra shredded mozzarella adds gooey richness that's hard to resist.

Can I use store-bought garlic aioli instead of making my own?

Yes, you can! Using a quality store-bought garlic aioli saves time and still tastes great. However, making it from scratch adds a fresher, more vibrant flavor that really enhances the sandwich.

How do I store and reheat leftover sliders without them getting soggy?

Store leftover sliders in an airtight container in the fridge for up to 3 days. Reheat in the oven at 375°F for about 10 minutes to keep the buns crisp and the cheese melty. Avoid microwaving as it tends to make the bread soggy.

Final Thoughts

These Buttery Roast Beef Sliders with Caramelized Onions Recipe isn’t just a meal—it’s a flavor-packed experience perfect for sharing or indulging in any day. With tender roast beef, sweet onions, melty cheese, and that irresistible garlic butter glaze, they hit all the right notes. Whether you’re making them for a cozy night in or a festive gathering, these sliders are sure to bring smiles and satisfied appetites. Happy cooking, and don’t forget to savor every buttery, beefy bite!