Mushroom Swiss Steakhouse Burger

Ingredients

• 2 pounds 80/20 ground beef, divided into 4 half-pound patties
• 2 tsp salt, pepper, and garlic rub (or to taste)
• 4 slices Swiss cheese
• 4 brioche buns, toasted
• Mayonnaise, for spreading
• 1 Tbsp olive oil
• 2 Tbsp butter
• 1 small yellow onion, diced
• 1 cup sliced mushrooms
• 1 tsp minced garlic
• 1 tsp salt, pepper, and garlic rub
• 1/4 cup Country Bob's All-Purpose Sauce