Peel the garlic and press it through a garlic press. Mix crème fraîche, cream, ketchup and garlic. Peel onions and cut them into rings. Wash the meat, dab dry and cut into approx. 2 cm thick slices.
Cut pork belly into thin slices, halve slices if necessary. Heat oil in a large pan. Fry the pork filet in portions on each side for about 2 minutes. Fill fillet and belly alternately into a greased casserole dish.
Spread the onions on top and pour the sauce over them. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 30 minutes. Serve with salad and bread.