Add butter, miso paste, chives, lemon zest, and garlic powder to a large mixing bowl.
Combine with a hand mixer on medium speed until smooth. Scrape down the sides of the bowl as needed.
Scrape onto a piece of plastic wrap, roughly in the shape of a log.
Roll the miso butter in the plastic wrap and twist the ends tightly to seal.
Refrigerate until ready to use. The butter is ready to use right away, but it slices most cleanly after it's been chilled for at least 30 minutes.
Notes
Storage Tips: Miso butter will keep for up to 2 weeks in the refrigerator, tightly wrapped in plastic wrap. You can also transfer it to an airtight container or scrape into a ramekin and cover with plastic wrap. For longer storage, freeze the wrapped log for up to 3 months.Expert Tips: Make sure your butter is truly softened. Cold butter won't blend smoothly and you'll end up with chunks of miso rather than a uniform mixture. Leave it out on the counter for about an hour before you start, or cut it into small pieces to speed things up. Grating it will soften it even more quickly!Refrigerating or freezing it into a log shape makes it easy to slice off exactly what you need. You can even slice it frozen without having to thaw all of it.