1. First chop the onion and make a marinade with mustard and ketchup, then season with salt and pepper.

2. Then slice the meat, but not all the way through, and spread the marinade between the slices.

3. Then carefully place the meat in a baking dish and bake, covered, at 200°C (390°F) for 50 minutes to 1 hour.

4. Now pour in the whipped cream and sour cream and cook uncovered for another 15 minutes. Done! Delicious meal!