01 -
Heat a large cast iron skillet over medium-high heat. Add the ground beef and let it cook undisturbed for a few minutes until a deep brown crust forms on the bottom. Then break it apart and continue cooking until all the beef is fully browned.
02 -
Remove the browned beef from the skillet, leaving the fat behind. Add the butter to the skillet, then toss in the diced onion, bell pepper, and minced mushrooms. Let them cook without stirring for 1-2 minutes to develop some color, then stir and continue cooking until the vegetables are nicely caramelized.
03 -
Return the cooked beef to the skillet with the vegetables. Stir in the ketchup, Worcestershire sauce, salt, and pepper, mixing everything together well. In a small cup, mix the beef broth with the cornstarch until smooth, then pour this mixture into the skillet. Stir continuously until the sauce thickens, about 3-5 minutes.
04 -
Turn off the heat and add the chopped Provolone cheese to the skillet. Fold it into the hot beef mixture, stirring until it's completely melted and creates a creamy, cheesy sauce that coats everything.
05 -
Toast your brioche buns under a broiler or in a toaster oven until they're lightly golden. For extra flavor, you can butter the inside of the buns before toasting them.
06 -
Spoon the hot cheesy beef mixture generously onto the bottom halves of the toasted buns, then cap with the top buns. Serve immediately while everything is hot and the cheese is still gooey.