Pre-heat oven to 325°F. Whisk powdered sugar and egg whites
together in a large mixing bowl until smooth. Add whole eggs,
vanilla extract and melted butter, and whisk until just incorporated.
Add flour and blend, but do not overmix. Spread mixture onto wax
paper or Silpat® . Partially bake cookies for 3 to 5 minutes.
Remove from oven and cut cookies into desired shape. Return to
oven and continue baking until golden brown, about 1 minute.