Place the flour in a bowl or on a flat surface, and make a well in the centre.
Place the cubed butter in the middle of the well and mix with your hands or with a pastry blender, until the mixture resembles small peas or coarse crumbs.
Make another well in the mixture and add the ground nuts, icing sugar, vanilla sugar, salt, and, to the very centre, the egg yolks.
By hand, combine and knead the dough. After a a few minutes, it will resemble a coarse mixture. In another minute or two, it will come together into a ball of dough.
Divide the dough in half and then shape each ball into a rope about 1-1/2 inches in diameter.
Wrap each rope in plastic wrap or waxed paper and refrigerate for 1 to 2 hours [no more than 24].
Preheat oven to 350°F and line 2 cookie sheets with parchment.
Working with one roll at a time, remove the dough from the refrigerator and slice off walnut-sized pieces. Roll each piece into a 3-inch rope. Use your palm and opposite pointer finger to shape each little rope into a crescent.
Place the crescents about a half-inch apart on a cookie sheet. [I can do 24 per sheet, or about half the batch / one rope!]
Bake 12 minutes, or until the tips of each moon have just begun to brown.
While the first batch of cookies is baking, mix the 1/2 cup icing sugar with the vanilla sugar packet for the "moon-dust" and set aside before forming your second sheet of cookies with the remaining dough.
Remove the first batch of baked cookies from the oven and allow to sit on the pan for 2 minutes.
Slide the warm cookies towards each other on the centre of the baking sheet [to conserve sugar] and, using a sieve and spoon or a tea-ball, coat the tops of the cookies liberally in the sugar mixture.
Cool completely. Repeat, as above, with the second batch of cookies. And ENJOY!
Cookies may be stored in an airtight container for up to a week. Though, it's unlikely you'll have them around that long!