Measure all of your ingredients before you begin. Mince the clove of garlic and grate the ginger.
Set a small sauce pot over low heat.
Combine all of the ingredients except for the butter in the pan and stir it well. It will take some time for the miso paste to soften and fully incorporate with the other ingredients.
One the mixture has come together and the garlic and ginger are fragrant, turn off the heat. For an extra smooth sauce, push the sauce through a strainer.
Transfer the smooth sauce back to the pan and turn the heat on to medium low.
Add ½ tablespoon of butter to the sauce and stir it in well. After the first portion of butter has melted and incorporated completely, repeat until all of the butter is added.