Mix 2 tablespoons of oil, mustard, pepper and honey. Finely chop the tarragon and stir into the mustard cream, except for something to garnish. Halve tomatoes and clove of garlic. Season the meat.
Heat the oil in a pan, briefly sear the meat on all sides. Finally fry the tomatoes and garlic.
Brush the fillet with the mustard cream and place on a baking sheet with the vegetables. Cook in the oven for approx. 4 hours.
Peel potatoes. Cook in boiling salted water for about 20 minutes. Warm the milk and butter. Drain the potatoes and mash to a puree with the crème fraîche and milk mixture. Season to taste with salt, parsley and nutmeg.