Wash the fillet, pat dry and cut into approx. 1 cm thick slices. Brush the fillets with mustard on both sides and fry briefly but hot. Cut the carrots and leek into slices. Cut the broccoli into florets. Cook all vegetables separately in boiling salted water for about 3 to 5 minutes, rinse and allow to drain.
Grease an ovenproof baking dish and arrange alternately meat and vegetables (in rows). Mix the crème fraiche, milk, cheese, salt and pepper into a sauce and pour over the meat and vegetables. Bake at 200 degrees in a preheated oven for about 25 minutes.