1 large sweet potato, thinly sliced
1 large potato, thinly sliced
1 onion, thinly sliced
4 tablespoons butter, divided
salt and pepper to taste
2 tablespoons all-purpose flour
3/4 cup vegetable broth
1 cup shredded mozzarella cheese
2 tablespoons dry bread crumbs
1 tablespoon dried parsley (optional)