Hampen

Method

1. Cut 150 g of skinless white fish into rough 2 cm pieces, running your fingers over them to pull out any pin bones. Soak the pieces in a bowl of cold water for 10 minutes to whiten the flesh and wash out blood, then drain and squeeze them firmly dry in a clean cloth. Wet fish makes a slack paste, so press out as much water as you can.
2. Put the fish in a food processor with 0.5 tsp of fine sea salt and blitz for 2-3 minutes, scraping down twice, until you have a completely smooth, tacky paste that clings to the blade. The salt is what draws out the protein and gives hampen its spring, so do not skip or shorten it. (In a suribachi, pound and grind for about 10 minutes.)
3. Peel 60 g of yamaimo and grate it on the fine side of a grater into a slippery white purée. Add it to the fish paste with 1 tsp of caster sugar, 1 tsp of sake, 1 tsp of mirin and 1 tsp of potato starch, and blitz or grind for a further minute until glossy and pale.