Technical Stages :

• Whisk the butter and sugar until pale. Combine with the egg yolks, vanilla extract and flour.
• Form little cylinders of dough and keep refrigerated (you may also prepare more dough and keep some cylinders in the freezer compartment).
• Before baking, glaze the cylinders with egg yolk and roll them in sugar.
• Cut in slices and alternate on a baking sheet protected by a sheet of baking paper.
• Bake at 180°C or 356°F for about 12 minutes.