Exists in two main variations: A 求肥-like variation, and one where 味噌 paste is piped into a hollowed out ゆず. The latter, I think, makes for a very nice 八寸!
Stuffed ゆず
Take a ゆず (or Amalfi lemon) and scoop out. Keep the lemon pulp to strain off some juice.
Blend together:
200 gr 味噌
100 gr brown sugar
50 gr lemon juice
50 gr walnuts
Fill lemons to ¾ (that's about 100 gr in a decently sized Amalfi lemon)
Steam for 1 hour
Dry for 1 month (but check every now and then, lest it dries out too much). There's a problem of case hardening akin to cured meat if you dry it in too dry an environment, so I'm using our cellar at 60% RH.