Draw snowflake designs on these cutout Christmas cookies with white and blue tinted icing. Powdered egg whites produce an icing that hardens when dried, so you can carefully stack the cookies to store or to give as gifts.
Whisk flour, baking powder and salt in a small bowl. Beat butter, sugar, egg, egg yolk and vanilla in a large bowl until blended. Stir in flour mixture. Gather into a ball; wrap in plastic. Refrigerate 2 hours.
Heat oven to 350°F. Roll out dough with lightly floured rolling pin on lightly floured surface to 3/8-inch thickness. Cut with 4-inch snowflake cookie cutter. Place on ungreased baking sheets, 1-1/2 inches apart. Bake at 350°F for 10 to 12 minutes, until lightly browned at edges. Remove cookies to rack to cool.
In a medium-size bowl, combine confectioners sugar, powdered egg whites and 2 tablespoons cool water. Beat on high with an electric mixer for 5 minutes, adding more water as needed for good piping consistency. Divide in half; tint half blue. Transfer icings to two separate pastry bags fitted with small writing tips. Decorate cookies with icing; sprinkle with sugar and nonpareils. Let icing dry 1 hour before stacking cookies.