Peel garlic and chop very finely. Peel and wash potatoes and cut into very thin slices. Spread potato slices on a tea towel and season with salt and pepper.
Grease a round casserole dish (approx. 24 cm Ø) and spread garlic in it. Layer the potato slices in a fan shape. Pour 200 g cream over it. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 45-50 minutes.
In the meantime clean and wash the beans. Cook in boiling salted water for about 8 minutes. Peel shallots and dice them very finely. Heat 2 tablespoons of oil in a saucepan. Add shallots and sauté. Deglaze with stock, bring to the boil and boil down for 5-6 minutes.
Stir in any sauce thickener, bring to the boil again. Season to taste with salt, pepper and sugar. Remove from the heat and fold in 4 portions of truffle butter, keep warm. Dab meat dry.
Place a slice of bacon on the edge of each fillet. Tie together with kitchen string. Heat 2-3 tablespoons of oil in a pan and fry the meat for 2-3 minutes on each side. Wash the marjoram, shake dry, put some stalks aside for garnishing.
Pluck the leaves from the remaining stems. Heat 1 tablespoon of oil in a frying pan, leaving out the ham cubes. Add the marjoram leaves. Drain the beans in a sieve. Add to the ham cubes and toss in.
Whip 100 g cream with the whisk of the hand mixer and fold into the sauce. Remove gratin from the oven and cut into pieces. Arrange meat, sauce, beans and a piece of gratin on plates, garnished with marjoram and Cape gooseberry.