Peel, wash and cut the potatoes into pieces. Pre-cook potatoes in boiling salted water for 10-12 minutes. Drain and leave to drain in a sieve. Peel onions and cut into thin rings.
Cut the bacon into thin strips.
Heat clarified butter in a large frying pan. Fry the potatoes in it, turning several times, for about 10 minutes until golden brown. Add the onions and bacon only shortly before the end of the frying time and fry with it. Season potatoes with salt and pepper.
Drain and halve the rollmops. Wash the dill, shake dry and pluck the flags. Arrange the fried potatoes and 3 rollmop halves on 4 plates and garnish with dill. Tartar sauce tastes good with it.