For the salad, wash and slice the tomatoes. Peel and halve onions and cut them into strips. Mix vinegar, salt, pepper and 1 pinch of sugar. Fold in 4 tablespoons of oil. Mix with tomatoes and onions.
Clean the mushrooms, possibly wash and halve them. Cut the meatloaf into thirds. Heat 1 tablespoon of oil in a large pan. Fry the Leberkäse for about 2 minutes on each side. Remove and keep warm.
Sauté the mushrooms in the hot frying fat while turning. Stir in sour cream, milk and mustard, bring to the boil briefly. Season to taste with salt and pepper.
In the meantime, slice the Parmesan cheese into shavings with a peeler. Wash parsley, shake dry, chop and stir into the mushrooms. Arrange the meat loaf with mustard mushrooms and tomato salad and sprinkle with parmesan.
It goes well with farmhouse bread.