Use this sweet, creamy filling in our Coconut Sandwich Cookies. This recipe also appears on the Martha Stewart Makes Cookies app for iPad.
Beat butter with an electric mixer on medium-high speed until creamy, about 2 minutes. Reduce speed to medium, and beat in confectioners' sugar, 1/2 cup at a time, scraping down side of bowl as necessary, until pale and fluffy, about 5 minutes. Add vanilla, and beat until smooth.