The Big Mushroom Melt Recipe

Form patties

Divide the 1 lb ground beef into two equal portions and gently form into two 4" patties about 3/4" thick. Do not overwork the meat. Make a shallow dimple in the center of each patty with your thumb to help them cook evenly.

Season both sides of each patty with kosher salt (1 tsp total) and freshly ground black pepper (1/2 tsp total). Pat the seasoning lightly into the meat. Brush 1 teaspoon vegetable oil on the outside of each patty or lightly oil the cooking surface to prevent sticking.

If using a stovetop skillet or griddle, heat it over medium-high heat until shimmering. If grilling, preheat to medium-high. Cook the patties 3-4 minutes per side for medium (adjust time for desired doneness). Avoid pressing down on the patties while cooking.

In the last 1-2 minutes of cooking on the second side, top each patty with two slices of Swiss cheese (4 slices total). Cover the skillet with a lid or use a tent of foil to help the cheese melt. Remove patties to a warm plate and tent lightly with foil to keep warm.

While patties cook, start the onions and mushrooms. Heat a large skillet over medium heat and add 1 tablespoon unsalted butter and 1 teaspoon olive oil.

Add the thinly sliced onion and 1/2 teaspoon granulated sugar. Cook, stirring occasionally, for 10-15 minutes until the onions are deeply golden and caramelized. If they begin to stick, lower heat and add a tablespoon of water to deglaze.

Push the onions to one side of the pan and add the sliced mushrooms (8 oz). Increase heat to medium-high and sauté mushrooms 4-6 minutes until browned and any released liquid evaporates.

Stir onions and mushrooms together, add 1 teaspoon balsamic vinegar, 1/2 teaspoon salt, 1/4 teaspoon black pepper, and 1/2 teaspoon fresh thyme leaves if using. Cook another 1-2 minutes to combine flavors. Taste and adjust seasoning.

Prepare buns: spread 1 tablespoon unsalted butter across the cut sides of the 2 buns. Toast buttered sides in a clean skillet over medium heat until golden, about 1-2 minutes. Remove and set aside.

Slice the tomato into 1/4" slices and pat dry with paper towel to reduce excess moisture. Wash and dry lettuce leaves.

Assemble each burger: place a lettuce leaf on the bottom bun, add a cheeseburger patty, pile a generous portion of the caramelized onions and mushrooms on top of the melted Swiss, add 1-2 tomato slices, then spread optional sauce on the underside of the top bun and place it on top. Serve immediately.

Mix 2 tablespoons mayonnaise, 1 teaspoon Dijon mustard, 1/2 teaspoon lemon juice, and a pinch (1/8 tsp) black pepper in a small bowl until smooth. Taste and adjust. Use about 1 tablespoon of sauce per burger or serve extra on the side.

Serve the Big Mushroom Melt hot with your choice of sides (fries, chips, or a simple salad). If making ahead, keep patties and mushroom-onion mixture warm separately and assemble just before serving so the buns remain crisp.