Peel the onions, cut them into slices and braise it lightly with frying oil in a pan for 5 minutes. Now add the wine vinegar and stir it until it is vaporised. Then stir in the creme fraiche and simmer it for another 5 minutes. Now stir in the mustard and season it with salt, black pepper and sugar. While it is simmering, cut the meat in 10 slices salt and pepper them a little and wrap them with the bacon slices. Now sauté the meat in the pan shortly from both sides and put them afterwards in a ligthly greased casserole dish. Baste the meat with the onion-mustard-sauce and bake it in the oven at 200°C for 45 minutes. As side dish it is best to serve rice or baguette and a green salad.