Caramelized Onion Steak and Garlic Aioli Sandwich
This caramelized onion steak sandwich is the kind of sandwich that makes you stop mid-bite and say something out loud. Thinly sliced medium rare steak, deeply caramelized onions cooked low and slow in butter until jammy and sweet, roasted red peppers, arugula or sprouts lightly dressed in vinaigrette, and torn burrata all layered on a toasted brioche bun slathered with a garlic aioli sauce built from aioli, Dijon mustard, stone ground mustard, and pesto. Every layer is doing something specific and together they produce a sandwich that is rich, bright, slightly tangy, and deeply satisfying in a way that justifies every minute of the 30-minute caramelized onion process.
A Quick Look At The Recipe
- Recipe Name: Caramelized Onion Steak and Garlic Aioli Sandwich
- Main Ingredients: The Garlic Aioli Sauce, garlic aioli, Dijon mustard, stone ground mustard, pesto, The Caramelized Onions, white onion, butter
- Why You'll Love It: This caramelized onion steak sandwich layers medium rare sliced steak, jammy caramelized onions, roasted red peppers, burrata, and a pesto Dijon garlic aioli on a toasted brioche bun.
It is messy and it is completely worth it. The burrata breaks open against the warm steak and the pesto aioli sauce drips down into the caramelized onions and there is no clean way to eat this sandwich and nobody minds because it tastes extraordinary. This is the sandwich for a Saturday lunch, a special occasion dinner, or any day that calls for something genuinely impressive that you made yourself.
Why You’ll Love This Recipe
Every element is intentionally chosen and intentionally placed. The sweet jammy onions balance the peppery arugula. The creamy burrata softens the richness of the steak. The pesto in the aioli adds a herby brightness that cuts through both. Nothing here is arbitrary.
The garlic aioli sauce with Dijon, stone ground mustard, and pesto is the condiment that makes this sandwich taste like it came from a restaurant. It is complex, slightly tangy, herby, and deeply savory all at once.
The brioche bun is the right call. Its slight sweetness and buttery richness hold up to the weight of every layer without getting soggy and they toast into something golden and slightly crispy that gives every bite a satisfying crunch.
The burrata is the detail that makes this sandwich unforgettable. Torn and placed warm over the steak it melts slightly into everything below it and adds a lush, creamy richness that no other cheese produces in quite the same way.
Ingredients Needed to Make Caramelized Onion Steak Sandwich
Intentional, quality ingredients. Here is what you need.
The Garlic Aioli Sauce
Garlic aioli is the creamy, garlicky base. Dijon mustard adds a sharp, slightly tangy edge. Stone ground mustard adds texture and a slightly more rustic, coarser mustard flavor that is different from the smooth Dijon alone. Pesto adds herby, garlicky, slightly sweet complexity that makes the whole sauce taste more developed than a standard aioli. Together they produce a condiment that could stand on its own.
The Caramelized Onions
A large white onion thinly sliced and four tablespoons of butter are all that is needed. The butter adds a richness that olive oil does not and produces a slightly more golden, more complex caramelized result. The salt draws moisture out of the onions during cooking and accelerates the caramelization process.
The Sandwich Components
Steak of your choice, medium rare and thinly sliced against the grain. Roasted red peppers from a jar or homemade add a sweet, slightly smoky, slightly acidic element. Burrata at room temperature torn over the top adds a lush creaminess. Arugula or sprouts dressed lightly in vinaigrette add a peppery, slightly bitter contrast. Toasted brioche buns hold everything together with a slightly sweet, buttery crunch.
How to Make a Caramelized Onion Steak Sandwich
1
In a small bowl, combine the garlic aioli, Dijon mustard, stone ground mustard, and pesto. Stir together until completely smooth and uniform. Taste and adjust the ratio of mustard to pesto based on your preference. Set aside at room temperature while you build the other components.
2
Melt the butter in a medium skillet over medium-low heat. Add the thinly sliced white onion and a generous pinch of salt. Spread into an even layer and cook over medium-low heat for 25 to 30 minutes, stirring every 3 to 4 minutes. The onions will go through several stages: first they will soften and turn translucent, then begin to shrink significantly, then slowly turn golden, then deep amber and jammy. Do not increase the heat to speed the process. High heat produces browned but not caramelized onions with a bitter edge rather than the deeply sweet, deeply golden, completely transformed result that low and slow produces. By the 30-minute mark they should be reduced to about one quarter of their original volume, deeply golden, and taste distinctly sweet rather than sharp.
3
Season the steak generously with salt and pepper on all sides. Heat a cast iron skillet over high heat until smoking or preheat the grill to high. Cook the steak to medium rare, about 3 to 4 minutes per side for a 1-inch thick steak. Remove from heat and let rest on a cutting board for a full 5 minutes before touching it. Resting is what keeps the juices inside the meat rather than losing them to the board when you slice. After resting, slice thinly against the grain for the most tender, sandwich-friendly pieces.
4
In a small bowl, toss the arugula or sprouts with just enough vinaigrette to lightly coat the leaves. They should taste bright and slightly acidic against the richness of the other components rather than overdressed.
5
Slice the brioche buns and toast cut-side down in the steak skillet with the residual butter and drippings, or in a toaster oven, until deeply golden and slightly crispy. Toasting the buns in the steak drippings adds an extra layer of flavor.
6
Spread a generous layer of the garlic aioli sauce on the bottom bun. Layer the caramelized onions directly on the sauce. Add the roasted red peppers over the onions. Layer the sliced steak over the peppers. Add the dressed arugula or sprouts over the steak. Tear the burrata directly over everything on the top layer and let it settle into the warm ingredients below. Add more garlic aioli sauce to the top bun. Press down gently and serve immediately.
Caramelized Onion Steak and Garlic Aioli Sandwich
Ingredients
- The Garlic Aioli Sauce
- 1/2 cup garlic aioli
- 1 tbsp Dijon mustard
- 1 tbsp stone ground mustard
- 2 tbsp pesto
- The Caramelized Onions
- 1 large white onion thinly sliced
- 4 tbsp butter
- The Sandwich
- 1 to 1 1/2 lbs steak of choice cooked medium rare and thinly sliced
- Roasted red peppers jarred or homemade
- Burrata cheese
- Arugula or sprouts
- Your favorite light vinaigrette for dressing the greens
- Brioche buns toasted
- Salt and pepper to taste
Instructions
- In a small bowl, stir together the garlic aioli, Dijon mustard, stone ground mustard, and pesto until smooth and well combined. Set aside.
- Melt the butter in a skillet over medium-low heat. Add the thinly sliced onions and a pinch of salt. Cook low and slow for 25 to 30 minutes, stirring every few minutes, until deeply golden, sweet, and jammy. Do not rush this step.
- Season the steak generously with salt and pepper. Cook in a hot cast iron skillet or on the grill to medium rare, about 3 to 4 minutes per side depending on thickness. Let rest for 5 minutes then slice thinly against the grain.
- Toast the brioche buns until golden and slightly crispy on the cut side.
- Toss the arugula or sprouts lightly in the vinaigrette.
- Build the sandwich. Spread a generous layer of the garlic aioli sauce on the bottom bun. Layer the caramelized onions, roasted red peppers, and sliced steak. Top with the dressed arugula or sprouts. Tear burrata over the top and add more sauce to the top bun before pressing it down.
- Serve immediately. It is messy and completely worth it.
Notes
Let the steak rest for 5 minutes before slicing. Cutting immediately loses all the juices onto the cutting board rather than keeping them in the meat.
Slice the steak thinly against the grain for the most tender, easy-to-eat result in a sandwich format.
The burrata goes on last and at room temperature. Cold burrata straight from the refrigerator does not have the same creamy, lush quality as one that has sat out for 15 minutes.
