Drain the herring, cut it into 1cm pieces and place in a ceramic dish.
Peel the apple and the onion. Cut the onion into halves and then into thin slices. Grate the apple on a middle-sized grater. Add the apple and onion to the herring.
Add the spices: sugar, grounded black pepper, mashed Jamaica pepper and the bay leaves; season the salad with salt, if needed.
Mix the salad with the greek yogurt and olive oil; cover and keep in the fridge overnight. Serve next day with warm cooked potatoes or a piece of rye bread.