Kurumi Soba

Method

1. Slide the kombu into a small pan of cold water and leave it there to soften while you build everything else.
2. Pound the walnuts and sesame seeds in a mortar, working from the outside in, until the grit collapses into a coarse oily paste that clings to the pestle.
3. Bring the kombu water up until bubbles cling to the sides of the pan and lift the kombu out before it can boil, then take the pan off the heat, sink the bonito flakes into it and strain the dashi once they have settled.
4. Warm the soy and mirin in the rinsed pan until the raw alcohol smell lifts off, then pour the dashi back in.
5. Beat the white miso into the nut paste, then let it down with the warm soy-dashi a spoonful at a time until it ribbons slowly off the spoon, and chill it.
6. Boil the soba in a deep pot of unsalted water until the strands are springy and taste of buckwheat rather than flour.
7. Drain the soba, wash the starch off it under a cold tap, and leave it sitting in iced water so the strands stay separate.
8. Cut the scallion into fine rings and tear the nori into narrow ribbons.
9. Drain the soba hard and heap it on a flat basket. Pour the walnut sauce into a separate bowl, scatter the scallion and nori over it, and dip a few strands at a time.