Dry-roast the walnuts in a frying pan over medium heat, stirring occasionally, until the kernels start to brown a bit and smell nice and toasty. Remove from the pan before they get burned. Let cool enough to handle, then wrap them up in a paper towel and rub them together until most of the outer skin is removed. Open up the paper towel and remove the skinned kernels. If there’s a bit of skin left on them there’s no problem, but removing most of the skin makes the nutty taste of the walnuts come through better. You can skip the skin-removing step if you like, but don’t skip the toasting part.

Once the walnuts are toasted and skinned, put them in a mortar and pestle, or better yet a food processor with chopping blade, and crush them up as finely as you prefer. I like it to be quite fine with a few small chunks. Add the mirin, miso and sugar and stir well until combined. (If you can’t find or can’t use mirin, either use the same amount of sake with a pinch more sugar, or just leave it out.)

Store in a tightly sealed container in the refrigerator for up to a week. To use, add as much as you like to blanched, boiled or steamed vegetables.