Ingredients

• 1 pound lean ground beef
  
• 2 tablespoons butter
  
• 1 small yellow onion, diced
  
• 1 small green bell pepper, diced
  
• 8 ounces brown mushrooms, minced
  
• 2 tablespoons ketchup
  
• 1 tablespoon Worcestershire sauce
  
• 1/2 teaspoon Kosher salt
  
• 1/2 teaspoon freshly ground black pepper
  
• 1 tablespoon cornstarch
  
• 1 cup beef broth
  
• 8 ounces provolone cheese slices, chopped
  
  • (Use 6 ounces if you prefer it less cheesy.)
    
• 6 brioche hamburger buns

Instructions

1. Heat a large cast-iron skillet over medium-high. Add the ground beef and allow it to brown undisturbed until a deep crust forms.
2. Break the beef apart and continue cooking until roughly half of it has that same browned crust.
3. Transfer the beef to a plate, leaving any drippings in the skillet. Add the butter, onions, bell peppers, and mushrooms.
4. Let the vegetables cook without stirring for 1–2 minutes to develop color. Stir, then repeat another 1–2 minutes of browning.
5. Return the cooked beef to the skillet.
6. In a small bowl, whisk the cornstarch into the beef broth.
7. Add the ketchup, Worcestershire sauce, salt, pepper, and the broth mixture to the skillet. Simmer 3–5 minutes, or until the mixture thickens and most solids sit above the sauce.
8. Turn off the heat. Stir in the provolone, starting with half and adding more until the mixture reaches your preferred level of cheesiness.
9. Spoon the filling onto toasted brioche buns and serve warm.