Prepare potatoes: Boil diced potatoes with salt until tender. Drain, add butter and parsley, mix well. Divide potatoes into 4 equal parts.
Cook ground beef mixture: Sauté onion and garlic in olive oil. Add ground beef, salt, paprika, and pepper. Cook until browned. Stir in tomato sauce.
Assemble casserole: Layer potatoes and ground beef mixture in a baking dish, ending with potatoes. Sprinkle with mozzarella cheese.
Bake: Preheat oven to 180°C (356°F). Bake casserole for 10 minutes or until cheese is melted and bubbly.
Serve: Let casserole cool slightly before serving hot.
