Wash the potatoes and cook covered for about 20 minutes. Quench, peel and let cool
Onions peel, finely dice. Wash the fillet, dab dry. Fry them in 2 tablespoons of hot oil all around for about 10 minutes. Season with salt and pepper, remove
Fry the onions in hot frying fat. Sweat flour in it. Stir in Calvados, 3/8 l water, cream and stock. Bring to the boil and simmer for about 5 minutes
Finely grate the cheese. Wash the thyme, remove the leaves. Cut potatoes and meat into slices and layer them in a greased casserole dish. Pour over the Calvados cream and sprinkle with thyme and cheese
Bake the gratin in a preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 25 minutes. Feldsalad tastes good with it
Drink: cool white wine