Herring: The recipe uses fresh herring filets. If you find smoked herring filets (called “matje”) you can also use them but rinse them first and make sure you marinate all the ingredients together for at least 12 hours. Another polite note on fresh herring: they say that it only keeps 1-2 days in the refrigerator. I read this when we were already on day 3 and counting. We went ahead and used the fish anyway but I’ll be honest that we were a bit on edge wondering which bite would be the one that would send us to examine the tiles around the toilet for the rest of the evening. In the end, we came out just fine, but next time I will use the herring sooner.