Peel, wash and slice the potatoes. Heat the oil in a large coated pan. Fry the potatoes for about 20 minutes while turning. Season with salt. Peel and chop the onions.
Add half of the onion cubes to the potatoes after about 12 minutes. Wash chives and parsley, dab dry and chop finely, except for some parsley for garnishing. Finely dice the gherkin.
Mix the salad cream, yoghurt, herbs, gherkin and remaining onion cubes. Season with salt, pepper and sugar. Arrange aspic, fried potatoes and tartar sauce on plates and garnish with parsley.