Mix the sugar with the salt and the spices and pour over the vinegar and water. Add a little lemon juice. Peel the onions, cut in half and cut into very thin slices. Mix everything together. Bring the marinade to the boil briefly and simmer on a low flame for 10 minutes. Remove from heat and let cool down completely.
Wash the herrings and pat dry. Cut open the pegs on the belly side, lay them on your belly and press them flat. Turn the pegs over and remove the center bone. Remove any other tangible bones, wash and dry again. Place the herrings with the marinade in a tightly sealable container, they must be completely covered with the marinade. Close the jar and let it rest for 4 days in the refrigerator.