Peel, wash and halve the potatoes. Cook in boiling salted water for about 20 minutes. Wash the meat and dab dry. Heat oil in a pan. Fry the meat in it in 2 portions on each side for about 2 minutes, place on a baking tray.
Place 1 slice of pineapple and 1 slice of cheese on each slice of Kasseler. Bake under the preheated grill for 3-4 minutes. Meanwhile drain the potatoes. Warm the milk, add it to the potatoes and mash it to puree, season with salt, pepper and nutmeg.
Stir in the fat. Wash the chives, shake dry and cut into rings. Arrange mashed potatoes and 2 slices of gratinated meat on plates. Sprinkle with chives.