Combine ground beef, bulk sausage, fine breadcrumbs, salt, ground pepper, Italian seasoning, and egg in a medium bowl. Mix well. Form into 4 flat patties.

Heat 1 tablespoon butter in a large pan over medium heat. Transfer meat patties to the pan and cook for 3 minutes. Flip meat patties and allow them to cook for another 3 minutes.

Pour marinara sauce onto the meat patties. Add 1 teaspoon chopped flat leaf parsley. Flip the patties to get them coated with sauce. Turn off the stove.

Place ciabatta (or focaccia) on a baking tray. Spread remaining butter onto each piece of bread. Place a meat patty on the top. Spoon remaining sauce in pan onto each of the patties.

Then top each patty with a slice of mozzarella to totally cover the bread. You may need to use more than one slice of mozzarella.

Broil sandwiches for 3 to 5 minutes or until cheese has melted and is golden.

Remove sandwiches from oven. Sprinkle with grated parmesan and remaining chopped flat leaf parsley.

Serve immediately.