Cut in cold butter into sifted flour. Add sugar and egg yolk one at a time. Only add two if dough is not moist and is too crumbly. Keep egg whites for glaze and set aside.
Knead dough with your hands for a few minutes. Wrap dough in plastic and let sit in refrigerator for at least 2 hours.
Roll out dough to ⅛ inch thick and cut out cookies with cookie cutters.
Place on cookie sheets with parchment paper and bake at 325 °F for 10 minutes.
Take out cookies with parchment paper and let cool on wire rack.
Meringue Glaze
Whisk egg whites and powdered sugar together on high speed.
Whisk glaze together until you make a thick mixture that does not run. It must not run or drip off a butter knife.