In a bowl whisk flour and baking powder. Keep aside.

In a different, bowl, whisk the butter with sugar until well combined, add the yolk and the vanilla, beat for three minutes.

Mix both dry and wet ingredients until combined. Make a cylinder 1 ½ inch in diameter. Cover with plastic wrap and refrigerate for one hour.

Preheat oven to 350F/180C.

Cut the cookies into eight equal size slices. Place a cupcake liner in a cupcake or muffin pan. Place the slices in the liners. Bake for 20 minutes or until golden.