Clean the mushrooms, wash if necessary, cut into slices. Peel and chop the onion. Dab schnitzel dry. Fry in hot clarified butter for 2-3 minutes on each side. Season with salt and pepper. Take out and keep warm.
Fry the mushrooms and onion in the frying fat for about 5 minutes. Season with salt and pepper. Dust with flour and sweat briefly. Add stock and cream while stirring, bring to the boil and simmer for about 5 minutes. Season to taste with salt and pepper.
Meanwhile cook the spaetzle in boiling salted water for 2-3 minutes. Drain. Melt butter in the pot. Swivel the spaetzle in it.
Arrange schnitzel with sauce and spaetzle. Sprinkle with fried onions. Serve with green salad with cream and lemon dressing.