Classic Polish marinated herring fillets in rich sour cream sauce with sweet diced apples, mild white onions, and lemon, served on crusty rye bread with fresh dill.
Soak the salted herring fillets in cold water or milk for 30 minutes to reduce saltiness. Drain, pat dry, and slice diagonally into 2.5cm bite-sized pieces.
In a bowl, combine the thick sour cream, lemon juice, sugar, salt, and white pepper, whisking until smooth.
Stir the finely diced apple and sweet white onion into the sour cream dressing, folding gently to coat.
Fold the herring pieces into the apple-sour cream mixture. Transfer to a glass jar or serving bowl, cover, and chill in the fridge for at least 2 hours so the herring absorbs the sweet and tangy cream.