In a large bowl, beat together the butter, powdered sugar, and vanilla sugar.
Mix in the egg yolks, then the flour and almond flour to form a dough.
Divide the dough into 3 equal pieces. Form each piece into a log about 1 inch (2.5 centimeters) thick and cover in plastic wrap. Refrigerate until chilled, at least 1 hour.
Preheat oven to 350˚F (180˚C). Line two baking sheets with parchment or lightly grease.
In a wide bowl, combine the powdered sugar and vanilla sugar.
Remove a chilled log of dough from the refrigerator and cut into 12 equal pieces.
Gently roll a piece into a rope with tapered ends and form into a crescent shape. Place on the prepared baking sheet. Repeat with remaining pieces, then remaining logs of dough, placing them 1 inch (2.5 centimeters) apart.
Bake in preheated oven until set and the bottom edges become golden, about 12 minutes.
Allow to cool on the baking sheet for two minutes.
While still warm, carefully transfer the cookies one at a time from baking sheet to vanilla sugar. Coat on all sides and place on wire rack. Repeat with remaining cookies and allow to cool to room temperature.
Once cooled, add one more coating of powdered sugar and store in an airtight container at room temperature for up to a couple of weeks.