Peel, wash and chop the potatoes and cook in boiling salted water for about 20 minutes. Peel and chop the onions. Drain cucumber and beetroot, collect liquid. Halve the pickled herring.
Heat 2 tablespoons of fat, lightly fry onions while turning. Dice corned beef roughly, add to onions and fry for approx. 2 minutes. Season well with salt and pepper. Wash the chives, shake dry and cut half into small rolls.
Drain the potatoes and add to the corned beef. Add 6-8 tablespoons beetroot juice and approx. 4 tablespoons cucumber water and mash to puree. In the meantime heat 1 tablespoon of fat in a large pan and fry 4 fried eggs.
Season with salt. Cut cucumbers fan-shaped. Arrange beetroot, cucumber fan, rollmop, lobscouse and one fried egg each on plates. Sprinkle or garnish with chive stalks and rolls.