01 -
Heat a large skillet over medium-high heat. Add the lean ground beef and sear for one minute without stirring, then break up and cook until fully browned. Remove beef from skillet and set aside.
02 -
In the same skillet, melt the unsalted butter over medium heat. Add diced yellow onion, green bell pepper, and brown mushrooms. Sauté for 5 to 7 minutes until vegetables are softened and golden.
03 -
In a mixing bowl, whisk together the beef broth, cornstarch, ketchup, Worcestershire sauce, kosher salt, and freshly ground black pepper until smooth.
04 -
Pour the prepared sauce into the skillet with sautéed vegetables. Stir well and allow mixture to come to a gentle boil for 3 to 5 minutes. Return browned beef to skillet and combine thoroughly.
05 -
Remove skillet from heat and stir in chopped provolone cheese until melted and creamy.
06 -
Lightly butter the inside of each brioche hamburger bun. Toast buns in a separate skillet over medium heat for 2 to 3 minutes until golden.
07 -
Fill the toasted buns generously with the cheesy beef mixture and serve immediately.