Onions peel, halve and cut into thin slices. Heat the fat in a large frying pan, fry over medium heat for 5 minutes while turning until transparent. Stir in vinegar and simmer for 1-2 minutes. Stir in crème fraîche and simmer everything over a low heat for 5 minutes. Stir in mustard and season to taste with pepper, sugar and a little salt.
Wash the fillet, dab dry and cut into 12-16 medallions. Press flat with your hand and season with pepper and paprika. Fold the slices of bacon 1x so that they are slightly larger than the fillet. Put 1 medallion on 1 bacon slice each. Then put them on the baking tray. Spread the onion mixture evenly on the meat. Bake on the middle shelf of the preheated oven (electric: 225 °C/ convection oven: 200 °C/ gas: level 4) for 15-20 minutes. Wash parsley, dab dry and chop finely. Sprinkle over the meat.
Then put them on the baking tray. Spread the onion mixture evenly on the meat. Bake on the middle shelf of the preheated oven (electric: 225 °C/ convection oven: 200 °C/ gas: level 4) for 15-20 minutes. Wash parsley, dab dry and chop finely. Sprinkle over the meat. Serve with salad and toasted bread
If you like, you can also cut the medallions a bit thicker and fry them in oil for 2-4 minutes before gratinating