Brush the lean pork belly slices well with medium-spicy mustard, season with salt, pepper and sprinkle with paprika. Then spread the sauerkraut on top, add the thinly sliced onion and 1 - 2 cloves and 1 bay leaf each. Roll up the 4 roulades and tie with kitchen twine.
Fry the roulades on all sides in hot oil (add the second onion). Deglaze with water (can also be meat stock and / or white wine) and let simmer on a low flame for about 30 - 40 minutes.
Thicken the sauce with flour butter, roux, sauce thickener or cornstarch to taste. Go with boiled potatoes, mashed potatoes