Brown hamburger meat and sausage together. Slice potatoes and put in bottom of 9x13-inch pan. Slice and break apart onion and put on top of potatoes. Put hamburger mix on top of potatoes and onions. Mix cheddar cheese and mushroom soups, milk and sauce together and pour over top of meat (may put pepperoni on top if you like) and potatoes. Bake covered in 375-degree oven until potatoes are tender. Remove cover and put mozzarella cheese on top. Return to oven for 10 minutes or until cheese melts.