Dice the butter and let it sit at room temperature to soften (do not use the microwave oven).
Cook the egg in boiling water for 5-7 minutes until hard boiled.
Then blend the egg yolk with the butter until the mixture is smooth and without lumps;
Sift the flour on a pastry board and make a well in the center. Put the baking powder, sugar, softened butter with the egg, vanilla extract, and a pinch of salt into the middle of the well of flour.
Mix and knead with your hands until you have a compact dough. Make a ball, wrap it in a dampened tea towel, and refrigerate for at least 30 minutes, longer if possible.
On a lightly floured surface roll out the dough to ¼ inch (5-6mm) thickness. Cut out the cookies using a flower cookie cutter and make a hole in the center with a straw or a small pastry tip. Knead the leftover dough and repeat the process until finished.
As soon as you cut the cookies, transfer them onto a baking sheet lined with parchment paper; Leave about 2 inches (5cm) between them.
Pre-heat the oven to 350°F (180°C) and bake for 10-12 minutes. Canestrelli should remain pale, so don’t think they have to be golden brown like other cookies.
Remove them from the oven and let them cool down before transferring them to a wire rack. Generously dust with powdered sugar. Eat and enjoy!