You can refrigerate the filling, covered, for up to one day; let it soften at room temperature before using.

Ingredients

　　1 stick (1/2 cup) unsalted butter, room temperature

　　2 cups confectioners’ sugar

　　1 tablespoon honey

　　3 tablespoons freshly squeezed ruby red grapefruit juice

　　In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and sugar until light and fluffy, about 4 minutes. Beat in the honey. Add juice, 1 tablespoon at a time, until filling holds together and is smooth and creamy, about 2 minutes. Transfer to a small bowl, cover, and set aside until ready to use.

　　Reprinted with permission from Martha Stewart's Baking Handbook by Martha Stewart. © 2005 Clarkson Potter