In the meantime, grease a flat casserole dish and place the Kassel slices next to each other. Mix the crème fraîche and cream well with the whisk in the mixing bowl.
Place the pre-browned hash browns on the Kassel slices, then spread the crème fraîche sauce over them well. Sprinkle with grated cheese and bake in the oven at 200 degrees for at least 30 - 40 minutes.