Peel and finely dice the onions. Clean, clean and slice the mushrooms. Dab meat dry. Wash the tomatoes. Peel and wash potatoes and cut them into sticks (type Pommes).
Heat 2-3 tablespoons of oil in a pan and fry the meat for about 1 minute on each side. Season with salt and pepper, remove and keep warm. Toss the tomatoes briefly in the pan. Add the mushrooms to the frying fat and fry while turning.
Add the onions and fry briefly. Season with salt and pepper. Deglaze with stock and cream. Let it boil down for about 5 minutes. Season with salt, pepper and sugar. In the meantime wash parsley, shake dry and chop finely.
Place the meat and tomatoes on an ovenproof dish and spread the mushrooms on top. Add the herb butter in flakes. Bake in the preheated oven (electric range: 225°C/ convection oven: 200°C/ gas: level 4) for 12-14 minutes.
In the meantime heat 1 litre of oil in a wide saucepan, fry the potatoes in it in 3 portions until golden brown. Keep warm. Season with coarse salt, take the fillet steaks out of the oven and sprinkle with parsley.
Add some fries.