Remove peel from potatoes, rinse and cut into pieces. Cook in 1 1/2 l salted water. Cut apples into pieces, remove the core and cook with a little water and sugar.
Drain the potatoes and put them in a big bowl. Pass the cooked apple pieces through a sieve and mix into the potatoes. Mix everything with a blender until smooth. Place again in a saucepan and heat.
Cut the bacon and onions into cubes, fry them in a frying pan and add them to the potato-apple mixture, season. Cut the blunzen into thick slices and fry them in hot butter on both sides. Serve with the apple-peanut mixture.