01 -
Get a big cast iron pan really hot on medium-high heat. Throw in your ground beef and let it sit until you see a nice brown crust forming on the bottom, then break it up. Keep cooking till about half the meat has that tasty dark crust for the best flavor.
02 -
Take out the beef but keep the drippings in the pan. Drop in your butter with the chopped onions, peppers, and mushrooms. Don't touch them for 1-2 minutes so they brown up nicely, then give them a stir and let them cook another 1-2 minutes until they're golden and sweet.
03 -
Put the beef back in with all those veggies. Mix your beef stock and corn thickener in a small cup until it's smooth. Pour this mix into the pan along with your ketchup, Worcestershire sauce, salt, and pepper, and stir everything together.
04 -
Let it all bubble away for about 3-5 minutes until it's not so runny anymore. You want a chunky, thick mixture, not something soupy or watery.
05 -
Turn off the heat and dump in your chopped Provolone. Stir until it's all melty and mixed through your beef and veggie mix.
06 -
Scoop this yummy Philly mixture onto your warm brioche buns and eat right away.