Dab the fillet of beef dry and cut into strips. Peel and quarter shallots. Clean and wash the celery (put some celery green aside) and cut into slices.
Clean, wash and slice the mushrooms. Peel, wash and roughly grate the potatoes. Mix with egg yolk and season with salt, pepper and nutmeg. Heat 10 g clarified butter in a pan and fry the meat briefly.
Remove and sauté the shallots, celery and mushrooms in the cooking fat. Deglaze with cognac, cream and stock and simmer for 5 minutes. Heat the rest of the clarified butter in a second pan and bake small golden-brown cookies from the grated potatoes by the spoonful.
Add the meat to the vegetables, season with salt and pepper. Add sauce thickener while stirring, bring to the boil again. Arrange the shredded meat and potato cookies on plates and garnish with celery green.