Cover herring fillets with water and soak for about 2 hours. Soak rolls in water.
Meanwhile wash the dill and cut it finely. Mix with lemon juice, sour cream and 2 tablespoons of sugar. Season to taste with salt and pepper. Wash the salad, drain well and tear into pieces. Drain capers.
Peel and wash the potatoes.
Peel and finely chop the onion. Dab herring fillets dry, chop very finely or puree them briefly. Squeeze the bread roll well. Knead everything with minced meat and 1 egg. Season with pepper. Form 8-10 meatballs with moistened hands.
Cook the potatoes in salted water for about 20 minutes. Put the meatballs in about 3 l boiling, slightly salted water and let them simmer at low heat for about 15 minutes. Lift out and keep warm. Approx. 3⁄4 l Measure out the cooking water.
Heat the butter and sauté the flour in it until light yellow. Stir in cooking water and bring to the boil. Add capers. Simmer sauce for about 5 minutes. Season with salt, pepper and 1 pinch of sugar. Whisk sour cream and 2 egg yolks.
Stir in 5 tablespoons of hot sauce, then stir into the rest of the sauce. Heat the meatballs in the sauce (do not boil any more!).
Wash and finely chop the parsley. Drain the potatoes and toss with the parsley. Mix salad and dill sauce. Arrange everything. Drink tip: beer, e.g. Mellenthiner Hell.