Sift the flour and knead it together with the egg yolk, butter, lemon zest, vanillina (or vanilla extract), sugar, salt and baking powder. You can do this in an electric mixer or by hand.
Make a ball with the dough, wrap it in cling wrap and put it in the fridge for 30 minutes.
Roll the dough into a 5 mm – 0.2 inch thick sheet and cut out flower shapes with a small hole inside (I used a little oil bottle cap to make the small hole).
Put the cookies on an oven tray covered with baking paper and cook them in a pre-heated oven at 190°C – 375°F for 10 minutes. The cookies have to be just a light golden colour.
Let them cool down on the tray. When they are completely cold, dust them with a generous amount of icing sugar.