Peel the potatoes, cut into thin slices and layer them together with the leek, 2 crushed garlic cloves, pepper and salt in a greased ovenproof dish.
Warm up the milk and cream and pour over it. Cover the mold with aluminum foil and let simmer for 30 minutes at 200 ° C in the oven on the lower rail.
Remove aluminum foil and bake for another 20 minutes. Pour in some milk if necessary.
Knead 2 tablespoons of butter with a crushed clove of garlic, put in the refrigerator.
Fry the fillet in margarine, pepper and cook covered on a low heat for about 20 minutes. Then add salt. Cut the tomatoes crosswise, press in flakes of butter, pepper, salt and grill for 5 minutes.
Cut the fillet into thick slices, place them in rows on the potatoes, garnish with garlic butter, add the tomatoes. Put the dish with the finished dish in the oven until the butter melts.