* 1 Tbsp. olive oil, divided
* 1 Tbsp. butter, divided
* 1/2 medium yellow onion, peeled, halved and sliced
* 1/2 lb. medium domestic mushrooms, stemmed and sliced
* 1/2 lb. cremini mushrooms, stemmed and sliced
* 1/2 Tbsp. chopped garlic
* 2/3 cup red wine
* 1/2 cup beef broth
* 1/2 cup heavy cream
* 1/2 tsp. sea or kosher salt
* 1/2 tsp. fresh ground pepper
* 4 (6 oz.) beef sirloin patties
* 4 tsp. crushed mixed peppercorns
* Sea or kosher salt
* 8 slices Sargento® Deli Style Sliced Medium Cheddar Cheese
* 4 hamburger buns (optional)
* 1. In a large skillet over medium-high heat, add half the olive oil and half the butter. Add onions and cook, stirring occasionally, until onions are light brown. Remove to plate and set aside. Add remaining oil, butter and mushrooms. Cook until liquid is evaporated and mushrooms are light brown. Add garlic and cook for 2 minutes. Add wine and simmer until liquid is almost completely evaporated. Add beef broth and simmer until almost all liquid is evaporated. Add cream and simmer until thick. Add salt and pepper. Keep warm.
* 2. Sprinkle each beef patty with 1 teaspoon crushed peppercorns and salt, and press peppercorns lightly into meat. Preheat cast iron skillet over medium-high heat. Add burgers, peppercorn-side down, and cook, turning once, to an internal temperature of 160?F. Top each burger with 2 slices cheese and melt. If using buns, toast buns lightly. Top burgers with mushroom mixture and serve.
