01 -
Heat a large cast iron skillet over medium-high heat. Add the ground beef and cook until a deep brown crust forms on the bottom before breaking it apart. Continue cooking until about 50% of the beef has developed a rich crust for maximum flavor.
02 -
Remove the beef from the skillet, leaving behind any rendered fat. Add the butter to the skillet along with the diced onions, bell peppers, and minced mushrooms. Allow to brown for 1-2 minutes without stirring, then stir and brown for another 1-2 minutes to develop caramelization.
03 -
Return the beef to the skillet with the vegetables. In a small cup, whisk together the beef broth and cornstarch until smooth. Pour this mixture into the skillet along with the ketchup, Worcestershire sauce, salt, and pepper, stirring to combine.
04 -
Cook the mixture until it thickens and becomes less liquidy, about 3-5 minutes. The mixture should be hearty and thick rather than soupy.
05 -
Turn off the heat and stir in the chopped Provolone cheese until completely melted and incorporated throughout the beef and vegetable mixture.
06 -
Pile the Philly Cheese Steak mixture onto toasted brioche buns and serve immediately.