1) In a skillet or a frying pan, heat the oil.
2) Sauté the beef for 2 minutes to seal it.
3) Coat the beef with mustard and dab it with crushed peppercorns.
4) Wrap the fillet tightly in a foil and freeze it for at least 2 hours.
5) Place the wrapped fillet in a roasting pan and bake it in a preheated oven for 25 minutes.
6) Shift the fillet to a board and open the foil, making sure that the pepper crust remains undisturbed.
7) Cover it with another board or a plate. Place a weight of X 450 g / 1 lib cans and refrigerate it overnight.
8) Slice the fillet into 4 mm / 1/6 and serve with potato salad.