Caramelized onions, mushrooms, and Swiss cheese smother this burger in a blanket of deliciousness. It’s easy to prepare, but looks like it’s from a fancy steakhouse. We served it on a decadent brioche bun and topped it all with a homemade truffle aioli. If you can’t find truffle oil, the sauce is just as delicious without it. You can also make homemade buns if you like!
Serve these babies on a weeknight or for a fun dinner party. Some crispy fries on the side are a must.
- For the Burgers:
- 5 tablespoons butter (divided)
- 1 small onion (thinly sliced)
- 2 teaspoons salt (divided)
- 2 cups mushrooms (sliced)
- 1 teaspoon Worcestershire sauce
- 1/2 teaspoon dried thyme
- 4 brioche burger buns
- 4 beef patties
- 1 teaspoon ground black pepper
- 1 cup Swiss cheese (or Gruyere, shredded)
- For the Truffle Aioli:
- 1/2 cup mayonnaise
- 1 teaspoon salt
- 1/2 teaspoon ground black pepper
- 1 teaspoon lemon juice
- 1/2 teaspoon truffle oil
- 1 clove garlic
Note: while there are multiple steps to this recipe, this recipe is broken down into workable categories to help you better plan for preparation and cooking.
Make the Burgers
Gather the ingredients.
Start by preparing the mushroom and onions. Heat a sauté pan on medium-high heat. Add 3 tablespoons of the butter, sliced onions, and 1 teaspoon of the salt. Sauté for 5 minutes, stirring frequently, until the onions become softened and slightly browned.
Push the onions to one side of the pan and add the mushrooms. Sauté until the mushrooms are browned and the onions are even softer, about 3 minutes.
Add the Worcestershire sauce and dried thyme and toss to combine. Cook for another minute and then remove from the heat and set aside.
Heat a cast iron pan on medium-high heat. Add the remaining 2 tablespoons of butter. Once melted, add the buns to the pan cut-side down and toast them until they are golden brown. You will probably have to toast them in two batches.
Salt and pepper both sides of the burgers with the remaining 1 teaspoon salt and all of the pepper. Keeping the pan at medium-high, cook the burgers for about 5 minutes per side until browned on both sides for medium doneness.
Make the Truffle Aioli and Assemble the Burgers
While the burgers are cooking, gather the ingredients for the truffle aioli.
Whisk together the mayo, salt, pepper, lemon juice, and truffle oil. Grate the garlic into the mixture using a microplane grater (or finely mince it) and whisk to combine.
During the last minute or two of cooking, sprinkle the tops of the burgers with some of the shredded cheese. Then divide the mushroom mixture among the four burgers and then top with the remaining shredded cheese. Cover the pan with a lid and cook for the remaining 1 or 2 minutes to allow the cheese to melt.
Slather the bun with the aioli.
Top the bun with the mushroom and cheese-coated burger and dig in.