Clean and trim the mushrooms and, depending on size, leave them whole, halve or quarter them. Peel onions and cut into cubes. Wash the meat, dab dry and season with salt. Heat the oil in a frying pan.
Brown the meat on all sides for about 10 minutes. Take out and sauté onions in the frying fat while turning for about 5 minutes. After 2 minutes add mushrooms. Deglaze with wine and fill up with stock.
Season with laurel. Add meat again. Stew in the closed roaster on the stove at medium heat for 2 1/2-3 hours. Turn meat over in between. Prepare spaetzle in boiling salted water according to package instructions.
Drain, drain well. Heat the fat in a pan. Fry spaetzle in hot fat for 5-10 minutes. Season to taste with salt, pepper and nutmeg. Cut cucumbers into strips. Remove the roast from the roaster and keep warm.
Stir flour and 4 tablespoons of water until smooth. Thicken the sauce with it, bring to the boil. Add cucumber and sour cream to the sauce. Season sauce with pepper, mustard and sugar. Cut meat into slices. Arrange meat, sauce and spaetzle.
Garnish with parsley.