Peel onion and garlic and cut into fine cubes. Heat 2 tablespoons of oil in a saucepan. Sauté onion, garlic and tomato paste. Add tomatoes and simmer for about 20 minutes. Season to taste with salt, pepper and vinegar.
Wash sage, shake dry, pluck leaves from the stems and chop. Mix the minced meat, eggs, breadcrumbs and sage, except for something to sprinkle on top. Season with salt, pepper and paprika. Form approx. 24 walnut-sized balls from the minced mass.
Heat 2 tablespoons of oil in a large frying pan and fry the meatballs for about 5 minutes, turning them over.
Grease the casserole dish (23 x 35 cm). Fill half of the tomato sauce into the dish, put Meatballs into the dish and pour the rest of the tomato sauce over them. Sprinkle with grated cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for about 20 minutes until the cheese is golden yellow. Sprinkle with remaining sage.