Season the fillet all over with salt and pepper.
Heat clarified butter strongly in a frying pan. Sauté the fillet in it all around. Sauté the rosemary, thyme and peppercorns briefly. 2.
Cover the bottom of a roasting pan with aluminum foil. Place the meat, herbs and peppercorns on top.
Place the roaster in the heated oven on the 2nd rack from the bottom. Roast the meat at 220 °C (circulating air 20 min. at 200 °C ) for 15 to 20 min.
In the meantime, for the sauce, rinse the grapes and remove the skin. Peel the red onions and cut them into thin strips. Peel and finely dice the shallots. Chop the parsley finely.
Heat 30 g butter in a sauté pan. Sauté the shallots in it, extinguish with vinegar and white wine, cook a little bit in 5 min at low temperature, pour through a sieve into another saucepan.
Toss in the cold butter 1 in small pieces.
4. at the same time, in a second frying pan, melt the remaining butter, sauté the red onions in it. Pour in the white wine sauce. Sauté the onions in it over medium heat for 5-8 min until they are soft. Finally, add the grapes and parsley, season with salt and pepper.
Remove the fillet from the oven, wrap in aluminum foil and rest for 10 minutes.
Cut the fillet open. Stir the gravy into the sauce. Arrange the meat on the sauce and repeatedly with the pepper mill over it.