1. Brown the Beef

Begin by heating a large cast-iron skillet over medium-high heat. Add the ground beef and allow it to cook undisturbed until a deep brown crust forms. This caramelization enhances the flavor. Once browned, break apart the beef and cook until 50% of it has a rich crust.

Remove the cooked beef, leaving any rendered fat in the skillet. Add the butter, followed by the diced onions, bell peppers, and minced mushrooms. Let them brown undisturbed for 1-2 minutes, stir, and repeat to develop a deep, rich flavor.

Return the beef to the skillet. In a small cup, whisk the beef broth with cornstarch until smooth. Pour this mixture into the skillet along with ketchup, Worcestershire sauce, salt, and pepper. Stir to combine everything thoroughly.

Allow the mixture to cook for about 3-5 minutes, or until it thickens and reaches a hearty consistency. You want a thick, rich texture rather than a soupy one.

Turn off the heat and stir in the chopped Provolone cheese until it's fully melted and coats the beef and veggies in a gooey, cheesy sauce.

Spoon the mixture generously onto toasted brioche buns and serve immediately. For an extra touch, garnish with fresh parsley or a sprinkle of red pepper flakes.