This is the method used by restaurants to whip butter to make it easier to spread, and for economical reasons to make butter go a lot further too. You can make it fancy like restaurants do by putting this mixture into a cake decorating tube with a fancy tip and pipe it into small dishes for individual servings. I have even used a plastic bag, cut off the corner, placed a fancy decorating tip in the corner, added the butter mixture and piped it into tiny dishes I got at the dollar store. One for each dinner guest is a nice touch.
I store the whipped butter in a glass covered container on the counter top in cooler weather. In warmer weather I store it in the refrigerator and bring it to room temperature before using.