Place in a food processor:
Process until the nuts gather into a ball, 2 to 3 minutes. Break up the ball with a spoon. If desired, add:
Process until the nuts release their oil and a butter forms. This generally takes 1 to 3 minutes but may take as long as 5 minutes, particularly if you are using almonds. Store the butter, covered, at room temperature for up to 2 weeks or refrigerate for up to 3 months.