Fully soften the butter by leaving it at room temperature for 30-60 minutes (or overnight) before proceeding.
Put softened butter in a small bowl and beat with a rubber spatula until it's fully malleable.Add the chives, orange zest, and salt. Beat again until the herbs are completely covered with butter.
To serve the same day:Pour butter into a serving bowl and refrigerate for at least an hour before serving. Note that butter will harden again in the fridge, so if you want it to be spreadable, take out of the fridge a few minutes before serving.Refrigerate leftovers and use within 5 days.To store for later:Freeze in a log: Chill butter until it's cool enough to form, and then roll it into a log. Use parchment paper or a rubber spatula to help you form the log. Wrap in parchment paper or plastic wrap, and store in an airtight container, and freeze for up to 6 months. When you're ready to use the butter, simply slice off the amount you want to use and put the rest back in the freezer.Freeze in portions: Scoop butter into portioned molds (like a silicone ice cube tray), and freeze until hardened. Pop the butter out of the molds, transfer to an airtight bag, and use the butter within 6 months.
Notes
Avoid wrapping the butter in wax paper, which (in my experience) tends to stick to the butter (especially when softening the whole log).Nutrition information assumes 1 tablespoon of butter per serving.