Preheat the oven to 80 °C. Warm up 1 platter and 4 plates in it.
Season the meat and sear it on both sides in cooking butter for 11/2-2 mins. Place immediately on the warmed plates and allow to finish cooking for 30-40 mins. The core temperature should be around 72-75 °C.
Steam the celery and carrots until al dente and drain. Cover and keep warm with the meat in the oven.
Deglaze the frying juice with wine or apple juice and reduce by half. Add the Noilly Prat and/or veal stock and simmer a little more. Add the cream and Vacherin Mont-d'Or AOP and beat the sauce until frothy with a hand blender. Season.
Pour the sauce on the warmed plates and serve two veal medallions and vegetables on each plate.