Fry the meat well in hot oil in a pan. In the meantime, cook the spaetzle in plenty of salted water until al dente and drain. Grease a baking dish and fill it with the drained spaetzle.
Peel the onion and chop finely. Put in a saucepan with a little butter, fry and sauté. Clean the mushrooms, cut into thin slices and add to the onion in the saucepan. Add the white wine and steam the mushrooms. Pour the cream into the mushroom and white wine sauce, add the chopped parsley and season with salt, pepper and sugar. Let the sauce simmer for about 5 minutes.
Place the meat on the pasta in the baking dish and pour the mushroom sauce over it. Sprinkle everything with the grated Emmentaler. Baked in the oven at 200 ° top / bottom heat for approx. 20 - 25 minutes until the cheese has run and is slightly browned.