These simple little cookies appear on store shelves around the holidays, but baking them yourself produces a rich buttery cookie that is perfect all year round.
Preheat oven to 325 degrees.
In the bowl of an electric mixer fitted with the paddle attachment, beat together butter and confectioners' sugar on medium speed until light and fluffy, about 3 minutes.
Add vanilla and egg, beat until just combined. Slowly add flour, and beat until well incorporated. Transfer dough to a pastry bag fitted with a 7/16-inch star tip.
Pipe 2 1/2-inch rings onto parchment paper-lined baking sheets, spaced 2 inches apart. Sprinkle cookies with plain decorators sugar.
Bake until lightly golden around edges but still light on top, about 20 minutes.
Transfer sheets to wire racks; let cool completely.