Rinse the herrings in cold water, pour over fresh water and set aside for 10 minutes. Repeat. Cut drained and dried herring into 2 cm pieces.
Dice the onions. Heat the oil in a frying pan, fry the onion. Add the chopped candied plums, bay leaf, allspice and cloves and fry with the onions for a further 3 minutes.
Add the tomato paste, paprika, marjoram and cinnamon and a good pinch of salt. Fry stirring until the paste darkens. Add vinegar, mustard, sugar and water. Bring the sauce to the boil, cook for about 5 minutes. Set aside to cool.
Dice the pickled cucumbers. Add together with the herrings and linseed oil to the sauce, stir and then season with salt if necessary. Put everything in a container and place in the fridge for at least 24 hours.