Herring is top secret.
Gravalux: There are various recipes on line and they are probably all good. You can’t go wrong since after the salt and sugar you can improvise and experiment on your own. A few days in the fridge and it’s ready. I tried adding dill and pickling spice during the process and when the gravalux was ready, I rinsed the salmon and cut into small chunks. I have also tried mixing the gravalux with mayo and onion and a little liquid for another day or so. Hmm Hmm.