1) Whisk the egg whites until soft peaks form. 2) Beat the egg yolks and butter until fluffy, an electric blender is really handy for this. Fold in 2/3 of the confectioner's sugar (reserve the rest for dipping the cookies into later) and the flour. Gently fold in the egg whites, they will collapse a bit, don't worry about it. 3) Preheat oven to 180C (350F) 4) The dough will be sticky, so you must moisten your hands from time to time while forming the cookies. 6) Bake in the middle shelf as you would other types of cookies for about 15 minutes.