Wash the potatoes and boil in their skins until tender. Let cool, then peel and cut into small pieces.
Peel the onion and cut into rings. Mix mustard with 1 tbsp. l. vegetable oil and pepper. Season potatoes with onions, mix and set aside. Wash sorrel and herbs, dry and chop.
Cucumbers cut into cubes, eggs - circles. Add cucumbers, eggs, herbs and pieces of herring to potatoes with onions, mix. Drizzle with vegetable oil.