1. Put sugar and meringue powder in the bowl of an electric mixer fitted with the paddle attachment; mix on low speed to combine. With the mixer running, add 3 tablespoons water. Raise speed to medium; mix, scraping down sides of bowl once, until icing is white and a ribbon forms when a spoon is lifted, about 4 minutes. (If necessary, thin icing with more water, a tablespoon at a time.)

2. To use, transfer to a pastry bag fitted with a small round tip (such as Ateco #2). Twist top of bag; seal with a rubber band. To keep icing from drying out, put a damp paper towel in the bottom of a tall glass; stand bag inside, tip end down.