Work butter and sugar with the tips of your fingers, then add egg yolks, flour, a pinch of salt and the vanilla essence. Knead the ingredients just enough to have a smooth dough and press it together to form a ball. Slightly flatten the dough, wrap it in cling film, then put it in the fridge for at least an hour. You can keep it overnight, too.
After one hour remove the pastry from the fridge, knead it again until easy to handle, then roll it out with a rolling pin and some rice flour in a 5 mm thick sheet.
Cut out round cookies with a 8 cm wide cookie cutter. Cut out a round window in half of the cookies with a smaller cookie cutter (or choose the shape you prefer). Knead again any left dough, roll it out again and cut more cookies.
Preheat oven to 180°C and bake the cookies in batches for 11-12 minutes, until lightly golden. Let them cool down completely on a wire rack.
Pair the cookies with a spoonful of jam. Dust them with icing sugar and enjoy, or store in a tightly closed box.