Salisbury Steak Burgers

Bahan-bahan (6 porsi)

• 1 ½ pounds ground beef
• ½ cup Panko bread crumbs
• 1 egg
• ¼ teaspoon black pepper
• 1 tablespoon all-purpose flour
• 1 ½ cups reduced sodium beef broth
• 1 ounce package brown gravy mix (dry)
• 2 tablespoons ketchup
• 1 teaspoon Dijon mustard
• 2 tablespoons butter
• 1 onion (thinly sliced)
• 1 cup mushrooms (thinly sliced)
• 2 tablespoons cornstarch
• 4 tablespoons water
• 6 large rolls (or Kaiser buns)
• 6 slices Swiss cheese (or cheddar cheese)