Henna Cookies Royal Icing 3 oz egg whites 1 tsp vanilla extract 4 cups confectioners sugar. Combine egg whites and vanilla and beat until frothy. Add confectioners sugar gradually and mix on low speed until sugar is incorporated and mixture is shiny. Beat on high until mixture forms stiff, glossy peaks, approximately 5 to 7 minutes. Add food coloring, if desired. Transfer to pastry bag and pipe. Store in airtight container in refrigerator for up to 3 days.