The Dutch call it maatjesharing, in Germany and Sweden it just matjes. It is made from young herrings caught before the breeding season started. I think the name is from the old word for young/unmarried women in German. We still have the word maid in Dutch. It’s meisje, and in English, maiden.
The fish is put in a brine and the pancreas stays in the fish, so the enzymes make the fish very soft.
In my area Matjes is prepared with raw onions and apples in a sauce of yogurt and cream. The dish is often served on Fridays in the early summer. It’s cheap and easy to prepare.
Image courtesy of bastian on Flickr.com.