For the gratin, peel the garlic, chop it coarsely and crush it with a fork. Wash thyme, shake dry, pluck off leaves and chop. Grate cheese finely. Sour Cream, 2⁄3 Mix cheese, garlic, thyme and cream.
Season with salt and pepper. Peel and wash the potatoes and cut or slice them thinly.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Place the potato slices with the sour cream sauce alternately in four ovenproof moulds (each containing approx. 200 ml) and press the individual layers well together.
Sprinkle with remaining cheese. Bake in the oven for 40-50 minutes.
For the meatballs, soak the toast in cold water and squeeze it out. Knead minced meat, mustard, barbecue sauce, egg and toast. Season with approx. 1 tsp salt, approx. 1⁄2 tsp pepper and paprika powder. Form 8 meatballs with moistened hands.
Heat 2 tablespoons of oil in a large frying pan. Fry the meatballs for 6-8 minutes on each side.
Wash the tomatoes. Peel onion, cut into rings. Turn the onion rings briefly in flour, knock off excess flour. Remove the meatballs from the pan and keep warm. Fry onion rings in hot frying fat while turning them golden brown.
Remove and keep warm as well. Add the tomatoes to the pan. Season with salt and pepper and then braise over medium heat for 5-7 minutes, stirring occasionally. Serve everything.