The recipe is from The Italian Kitchen by Gabriella Mariotti.
Polpette with Mozzarella and Tomato
1/2 slice white bread, crust removed
3 tablespoons milk
1-1/2 pounds ground beef
1 egg, beaten
2/3 cup dried break crumbs
vegetable oil, for frying
2 beefsteak or other tomatoes, sliced
1 tablespoon chopped fresh oregano
8 ounces mozzarella cheese, cut into 6 slices
6 canned anchovy fillets, drained and cut in half lengthwise (you could leave this out. we love it)
salt and ground black pepper
Preheat the oven to 400˚F. Put the bread and milk into a small saucepan and heat very gently until the bread absorbs all the milk. Transfer the bread to a bowl, mash it to a pulp and let cool.
Put the ground beef in a bowl with the bread mixture, the egg and seasoning. Mix well, then shape the mixture into six patties. Sprinkle the bread crumbs onto a plate and dredge the patties, coating them thoroughly.
Heat above 1/4 inch oil in a large frying pan. Add the patties and fry for 2 minutes on each side, until brown. Transfer to a greased ovenproof dish, in a single layer.
Lay a slice of tomato on top of each patty, sprinkle with oregano and season with salt and pepper. Place a mozzarella slice on top of each. Arrange two strips of anchovy, placed in a cross, on top of each slice of cheese.
Bake for 10-15 minutes, until the cheese has melted and the patties are cooked through. Serve hot, straight from the dish.