Cut the sirloin into slices. Roll up with 1 slice of pork belly each. Put in a flat baking dish. Roughly cut the onions and place them on the loin. Mix the cream, sour cream and 3/4 of the curry ketchup in a bowl (use less or more ketchup, depending on your taste). Pour the sauce over the loin. Salt and pepper are not necessary. Cook in the oven at 200 degrees for about 1 hour.
Pasta, rice or just plain white bread with it.
Tip: Fresh red peppers can also be used instead of onions.