1:Place all of the seeds in a large bowl. Pour over the beer, stir, cover with clingfilm and leave at room temperature overnight.
2:The next day, tip the mustard seeds through a sieve over a bowl. Put half in a blender and blitz to break down the mixture, then return to the bowl along with the whole seeds.
3:Add the sea salt, malt vinegar and honey. Stir thoroughly and spoon into sterilised jars.