1-First, prepare all ingredients by mixing 1 cup chicken broth, 2 tablespoons steak sauce, and 1 tablespoon Dijon mustard in a medium bowl; set aside.

2-Next, in a 12-inch skillet, cook 1 lb ground beef over medium-high heat for 7 to 8 minutes, stirring frequently until browned; drain and set aside.

3-Then, add 2 tablespoons butter to any remaining drippings in the skillet and mix in 8 oz thinly sliced mushrooms, 1 cup coarsely chopped white onion, and 1 teaspoon Montreal steak seasoning; cook for 7 to 8 minutes until onions are translucent and mushrooms are browned.

4-Continue by sprinkling 2 tablespoons all-purpose flour over the vegetables and cook for 1 to 2 minutes until the flour browns and smells nutty.

5-Return the beef to the pan and stir in the broth mixture, then bring it back to a simmer and cook for 3 to 4 minutes until thickened.

6-Finally, place about 1/3 cup of the mixture over the bottom half of each of the 8 regular-size burger buns, top with 1 tablespoon of shredded sharp Cheddar cheese, and add the top bun.