Remove the outer covering from the steak and save for later use in a ragout. Once the steak is clean, soak for one hour in olive oil, then brown on all sides in a frying pan and cover in the croute. Finish cooking on the grill.
Soak the mushrooms (girolles, morels, greys, chanterelles) in lukewarm water with a squirt of cognac. Finally slice the green onion and baste in butter in a frying pan. Put the mushrooms on with the green onions and cook for 3 minutes.
For the croute: Mix the herbs ( tarragon, chives, coriander, thyme and sage), the olive oil, the Guerande’s salt, the piment d’Espelette and assorted dry mushrooms. Wrap the beef in the croute and finish cooking on the grill.
To serve: Place a medallion of fillet steak with the croute and garnish with the mushrooms sautéed in butter. Decorate the sides of the plate with reduced beef stock.