Chanterelle Gratin with Beef Fillet and Grilled Sour Honey Shallots

1/3 Beef fillet (whole piece), approx. 1 kg floury potatoes, 50-80 g dried or 400 g fresh chanterelles, 1 onion, 1 clove of garlic, approx. 150 g butter, approx. 150 ml cream, approx. 1 liter milk, 150 g cheese (Parmesan or Gruyère), shallots, fresh thyme, honey, balsamic vinegar, salt, pepper.

1. Season the beef fillet with salt and pepper, then place it in a roasting pan and cook in a preheated oven at 70°C for 1-2 hours. 2. For the gratin, peel the potatoes and slice them thinly with a mandoline. 3. Soak dried chanterelles in hot water for 1 hour. Clean fresh mushrooms and tear them lengthwise into pieces. 4. Finely chop the onion and garlic and sauté them in 150 g of butter in a pot. Add the cream and milk, and bring to a gentle simmer. Add the potato slices and mushrooms and let them cook over low heat for about 20 minutes until the potatoes are tender. 5. Transfer the potato-mushroom mixture to a baking dish and sprinkle the grated cheese on top. Bake in the oven at 170°C until the gratin is golden brown. 6. For the shallots, peel them and place them on a bed of thyme in a small oven-safe dish. Drizzle with honey, balsamic vinegar, salt, and pepper, and place them in the oven with the gratin. 7. About 10 minutes before the gratin is ready, remove the beef fillet from the oven. Heat a pan and sear the meat on all sides (3-5 minutes per side) until it reaches the desired doneness. 8. Slice the beef fillet and serve with the gratin and grilled shallots.