Mushroom-swiss Burger Recipe

Form patties

Divide the ground Angus beef into two equal portions (about 8 oz each). Gently form into patties about 3/4–1 inch thick and slightly wider than your buns. Do not overwork the meat. Press a shallow dimple in the center of each patty to prevent puffing while cooking.

Season

Just before cooking, season both sides of each patty with kosher salt and freshly ground black pepper.

Cook patties

Heat a cast-iron skillet or griddle over medium-high heat and add 1 tablespoon neutral oil. When the oil is shimmering, cook the patties 3–4 minutes on the first side without moving them, until a good sear forms. Flip and cook 3 minutes more for medium-rare to medium. In the last 1–2 minutes of cooking, place two Swiss cheese slices (one per patty) on top of each patty and cover the pan for about 1 minute to melt the cheese. Remove patties and tent with foil to rest while finishing other components.

Prepare vegetables

While the patties rest or before cooking them, wipe any dirt from the portabella slices with a damp paper towel and slice them about 1/4-inch thick. Thinly slice the yellow onion into half-moons.

Caramelize onions

In a large skillet over medium-low heat, melt 1 tablespoon butter with 1 tablespoon olive oil. Add the sliced onions and a pinch of salt. Cook slowly, stirring occasionally, for 15–20 minutes until golden and softened. Sprinkle 1 teaspoon granulated sugar and continue to cook 5–10 minutes more, stirring, until deeply caramelized. If desired, add 1 teaspoon balsamic vinegar toward the end to deglaze and add depth. Remove onions to a bowl and keep warm.

Sauté mushrooms

In the same skillet (increase heat to medium-high), add a little additional oil if needed and add the sliced portabella mushrooms. Sprinkle with 1/2 teaspoon salt, 1/4 teaspoon black pepper and 1/2 teaspoon thyme. Cook, stirring, until the mushrooms release their liquid and brown at the edges, about 6–8 minutes. If they look dry, add a splash of water or a teaspoon of butter. Combine mushrooms with caramelized onions or keep them separate and warm until assembly.

In a small bowl, combine 1/2 cup mayonnaise, finely grated or minced garlic, 1/2 teaspoon fresh lemon juice, 1/2 teaspoon white truffle oil, 1/4 teaspoon Dijon mustard, 1/4 teaspoon salt, and a pinch (1/8 tsp) of black pepper. Whisk until smooth and taste; adjust salt, lemon, or truffle oil to preference. Refrigerate until ready to assemble.

Toast buns

Butter the insides of the split buns (about 1 tablespoon butter total). Toast cut-side down in a clean skillet or on the griddle over medium heat until golden, about 1–2 minutes.

Build the burger

Spread about 1–2 tablespoons of white truffle aioli on the bottom bun. Add a small handful (about 1/2 cup) of baby arugula or lettuce if using. Place the Swiss-topped patty on the bun, then pile on a generous portion of the sautéed portabella mushrooms and caramelized onions. Spread a little extra aioli on the top bun if desired and close the sandwich.

Serve

Serve immediately while hot. Optionally serve with fries, chips, or a side salad.