Peel the potatoes and boil them in salted water, mash them, add a little butter, then milk, a little sugar, salt and nutmeg to taste.
Cut the meat into fine strips. Fry the onion with the meat, season with salt, pepper and approx. 3 cm tomato paste and add the sliced mushrooms.
Sear it nicely, deglaze with cream, add a little water or milk if it gets too thick.
Let the whole thing simmer for about 20 minutes, season to taste again, then place in a high baking dish. Cover the strips with the mashed potatoes. Now sprinkle the cheese on it and put it in the oven until the cheese has melted nicely.