Boil the potatoes, peel them and let them cool down. Then cut into thin slices.
Season the cream with salt, pepper and horseradish. Layer half of the potatoes in a buttered baking pan like a rosette. Pour half of the seasoned cream on top. Lay the salmon evenly on top. Then layer the rest of the potatoes on top like a rosette and pour the rest of the cream over them. Sprinkle a few flakes of butter on top and bake in the oven at 220 degrees for about 25 minutes.
Sprinkle the gratin with parsley and serve. Lamb`s lettuce goes well with it.