Meanwhile, make the frosting. In a stand mixer with a paddle attachment, add powdered sugar and meringue powder to mixer bowl. On medium speed, add 1 tablespoon of water at a time until desired consistency is achieved. You want the frosting to be thin enough to melt within the outline of the cookie, but not so thin that it runs over the edges. If too thick, add warm water a teaspoon at a time to thin. If too thin, add powdered sugar to thicken.