Honey-miso Mayonnaise

1. Combine the egg yolk, miso paste, vinegar, and honey in a tall narrow cup that will just fit the head of your immersion blender. Carefully pour in the oil, so that it floats on top of the other ingredients. Insert the blender into the bottom of the cup, turn on the blender, and slowly draw the head up through the oil: a thick emulsion should form as you do so. Transfer the mayonnaise to a bowl and whisk in more vinegar and honey to taste.
2. Add up to 1 tablespoon water to thin the sauce to the desired consistency. It should be thick and cling to your finger or a spoon but not feel pasty or waxy on your tongue.