Cut butter into cubes and chill. Clean the chanterelles, wash thoroughly and drain well. Clean the mushrooms and cut them into slices. Peel and chop the onion. Wash the thyme, dab dry and pluck the leaves, except for something to garnish.
Wash pork fillets and pat dry. Heat 3-4 tablespoons of oil in a large pan and fry the fillets for about 8 minutes, turning them over. Season with salt and pepper, remove from the pan and leave to rest. Add the mushrooms and onion to the hot frying fat, also fry well and season with salt, pepper and thyme. Put 200 ml cold water into a small pot and stir in the sauce powder with a whisk. Bring to the boil briefly while stirring and turn off the heat. Gradually add cold butter to the sauce and remove from the heat. Cut pork fillets into slices and line a greased gratin dish with them in a fan shape. Stir the hollandaise sauce into the mushrooms and pour over the fillets. Bake in the preheated oven (electric range: 225 °C/ convection oven: 200 °C/ gas: level 4) for approx. 15 minutes.
Gradually add cold butter to the sauce and remove from the heat. Cut pork fillets into slices and line a greased gratin dish with them in a fan shape. Stir the hollandaise sauce into the mushrooms and pour over the fillets. Bake in the preheated oven (electric range: 225 °C/ convection oven: 200 °C/ gas: level 4) for approx. 15 minutes. Heat 4 tablespoons of oil in two large pans and fry the Rösti for approx. 8 minutes, turning them over. Sprinkle the finished fillet gratin with fresh thyme and garnish. Serve with Rösti
With 8 people: