Briefly rinse the porcini mushrooms with cold water and soak in 1 / 4l of hot water. Peel and wash the potatoes and kohlrabi. Cut into bite-sized pieces of the same size. Pre-cook in a good 1/2 l of boiling salted water for about 10 minutes. Lift both out and drain. Catch vegetable water, approx. 1/2 l.
Pat the schnitzel dry and cut into fine strips. Peel onions and cut them into fine pieces. Rasp cheese. Heat oil in a pan. Fry the meat vigorously all around in portions. Fry the onion briefly. Season everything and take it out.
Heat 20g fat in the frying fat. Sweat the flour in it while stirring until golden yellow. Add the mushrooms with the liquid, cream and vegetable water while stirring, bring to the boil. Melt half of the cheese in it. Season to taste with salt and pepper.
Spread the vegetables and meat in an ovenproof dish. Pour sauce over it. Sprinkle with the rest of the cheese and bake in a preheated oven at 200 ° C for about 20 minutes. Chop the chervil or parsley and sprinkle over the schnitzel pan.