1 litre of very good cultured cream (double cream will do but for a great butter it must be from a single herd).
16 gms sea salt – texture as fleur de sel.
16 gms dried seaweed – Nori.
Put the cold cream into a chilled mixer bowl (Stephen uses a Kenwood) and beat it at high speed. The cream will start to clump together and give off the buttermilk. It will start to splash everywhere so turn the speed down and allow the butter fat and butter milk to separate at low speed. Drain off the buttermilk and add the salt and dried seaweed. Then mix at low speed until the butter is an even colour and the salt is incorporated.
Put the butter on wax paper and work it to release the last of the buttermilk by kneading the butter. Wrap the butter in fresh wax paper and leave to set in the fridge.