Mushroom Swiss Burger Recipe

Prep & Fry

Cut russet potatoes into 1/4–3/8 inch fries. Rinse thoroughly in cold water, then soak 15–30 minutes to remove excess starch. Pat completely dry with a towel. Heat beef tallow in a heavy pot or deep fryer to 325°F (163°C). Fry potatoes in a single layer (working in a small batch) for 3–4 minutes until tender but not browned. Remove and drain on paper towels. Increase oil temperature to 375°F (190°C) and return fries to the hot tallow; fry 2–3 minutes until golden and crispy. Drain on paper towels and immediately season with 1 tsp salt. Keep warm until serving.

Cook mushrooms

Heat a large skillet over medium-high heat. Add 1 tsp olive oil and 1 tbsp butter. When foaming subsides, add sliced mushrooms in a single layer—cook without moving for 2 minutes to develop color, then stir. Add minced shallot and garlic; sauté 1–2 minutes until fragrant. Add Worcestershire sauce and thyme, then season with 1 tsp salt and 1/2 tsp black pepper. Cook another 1–2 minutes until mushrooms are tender and juices are mostly evaporated. Remove from heat and keep warm.

Form and cook patties

Preheat a heavy cast-iron griddle or large skillet over high heat until smoking hot. Lightly oil the surface with 2 tsp neutral oil. Divide ground beef into four loose 4 oz balls (do not overwork). Place two balls on the hot griddle about 3 inches apart (you will do two-on batches). Using a sturdy spatula or burger press, smash each ball flat to roughly 1/4 inch thickness, pressing firmly to get good contact. Season the exposed meat with a pinch of kosher salt and black pepper immediately. Cook without moving for 1.5–2 minutes until edges brown and juices appear. Flip the patties and immediately top each with a slice of Swiss cheese; cook another 30–60 seconds until cheese melts and patties finish cooking. Repeat with the remaining two balls.

Toast buns

While the second set of patties cooks (or after all patties are cooked), melt 2 tbsp butter in a skillet over medium heat. Split brioche buns and toast cut sides in butter until golden, about 45–60 seconds. Remove from heat.

Assemble each burger: spread 1 tbsp mayonnaise on the bottom bun and 1 tsp Dijon mustard on the top bun. Place one smashed patty with melted Swiss on the bottom bun, then top with a generous spoonful (about 2–3 tbsp) of sautéed mushrooms, a few rings of thinly sliced red onion, then place the second smashed patty on top. Cap with the mustard-spread top bun.

Serve each burger immediately with a 1/2 lb portion of hot fries cooked in beef tallow.