Mushroom Swiss Burger Caramelized Onions (Printable)

Juicy beef patty with sautéed mushrooms, Swiss cheese, and sweet caramelized onions served on a toasted bun.

# What You'll Need:

→ Burger

01 - 1 lb (16 oz) ground beef (80/20 blend preferred)
02 - 1 tsp kosher salt
03 - ½ tsp freshly ground black pepper
04 - 1 tsp Worcestershire sauce

→ Caramelized Onions

05 - 2 large yellow onions, thinly sliced
06 - 1½ tbsp unsalted butter
07 - 1 tbsp olive oil
08 - ½ tsp salt
09 - ½ tsp sugar

→ Mushrooms

10 - 8 oz cremini or button mushrooms, sliced
11 - 1 tbsp unsalted butter
12 - 1 clove garlic, minced
13 - ¼ tsp salt
14 - ¼ tsp black pepper
15 - 1 tsp fresh thyme leaves (optional)

→ Assembly

16 - 4 slices Swiss cheese
17 - 4 brioche or hamburger buns, split
18 - 2 tbsp mayonnaise (optional)
19 - Lettuce leaves (optional)

# Steps:

01 - In a large skillet over medium heat, melt butter with olive oil. Add sliced onions, salt, and sugar. Cook, stirring frequently, for 20-25 minutes until onions are deep golden and caramelized. Remove from heat and set aside.
02 - In the same skillet, melt butter over medium heat. Add sliced mushrooms and cook 6-8 minutes until moisture evaporates and mushrooms brown. Stir in garlic, salt, pepper, and thyme if using; sauté 1-2 minutes more. Remove and keep warm.
03 - Combine ground beef, Worcestershire sauce, salt, and pepper in a bowl. Gently mix and divide into four equal patties. Press a slight indent into the center of each patty to prevent puffing during cooking.
04 - Heat grill or skillet over medium-high heat. Cook patties 3-4 minutes per side for medium doneness or until desired level. Place Swiss cheese slices on patties during the last minute, cover to melt.
05 - Lightly toast brioche or hamburger buns on the grill or in a toaster until golden.
06 - Spread mayonnaise on the bottom buns if using. Layer with lettuce leaves, cooked patties topped with Swiss cheese, sautéed mushrooms, caramelized onions, and finish with top buns. Serve immediately.

# Expert Tips:

01 -
  • The Swiss cheese melts into buttery richness while the caramelized onions add a subtle sweetness that tastes like you spent all day cooking.
  • You can prep the toppings while the burgers cook, making it feel effortless even though every layer tastes intentional.
  • This is the burger that converts people who think they don't like onions or mushrooms—the cooking transforms them into something almost dessert-like.
02 -
  • Don't skip the indent in the center of each patty—it seems small, but it prevents the burger from swelling into a ball shape and ensures even cooking.
  • Caramelizing onions truly takes 20-25 minutes, and no amount of high heat will speed this up without burning them; the slow process is what creates that complex sweetness.
  • Toast your buns—it seems optional but it's the barrier between a soggy burger and a perfect one.
03 -
  • If your buns threaten to get soggy, spread a thin layer of mayo or butter on the inside to create a moisture barrier—this simple step makes a surprising difference.
  • Letting your ground beef sit at room temperature for 10 minutes before shaping helps it form more evenly and cook more consistently.

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