Savory Mushroom Swiss Burger (Juicy Steakhouse Style)

Ingredients

• 1 tablespoon unsalted butter
• 1 tablespoon olive oil
• 12 oz (340 g) cremini mushrooms, sliced
• 1/2 small yellow onion, finely chopped
• 2 cloves garlic, minced
• 1 tablespoon Worcestershire sauce
• 1/4 cup (60 ml) beef broth
• 1/2 teaspoon dried thyme
• 1/4 teaspoon black pepper
• Salt, to taste
• 1 1/2 lb (680 g) 80/20 ground beef
• 1 teaspoon kosher salt
• 1/2 teaspoon black pepper
• 4 slices Swiss cheese
• 4 brioche or potato burger buns, split
• 2 tablespoons mayonnaise
• 1 teaspoon Dijon mustard
• 4 lettuce leaves, optional