Holiday Swirl Shortbread Cookies

"Get ahead of the holidays with this make-ahead recipe that’s easy enough for a novice baker! It all starts with the tried-and-true shortbread formula: sugar, butter and flour. These three basic ingredients—plus a dash of vanilla—are all that’s needed to make a dough that bakes up into almost inexplicably buttery and tender cookies, so they’ve got substance, as well as style. Their swirled look is the result of a little bit of food color and Betty’s clever technique. Dough gets divided into three parts, ..."