Pour the flour onto your work surface. Add the nuts and powdered sugar and lightly mix these together with your hands or a fork. Make a well in the center of the flour mixture and put the egg yolk in it. Using a fork, mix the yolk with some of the flour mixture to make a thick paste. Sprinkle the butter cubes over the remaining flour mixture and rub the butter pieces into the flour with your fingers until there are only small shreds of butter left (or you can do the same using a pastry cutter if your prefer). Knead all of the ingredients together into a smooth dough. Wrap the dough in plastic wrap and allow it to rest at room temperature for 1 hour.

Preheat oven to 325°F (160°C). Grease baking tray(s) with butter. Working on a floured surface, roll egg-sized balls of dough into logs the thickness of a finger or thumb, cut small pieces off the log and roll these into little logs which you bend to make a crescent. Place crescents on greased baking sheet and bake for 10-12 minutes, until the tips of the crescents turn golden brown.

For rolling: stir powdered sugar and vanilla sugar together. Roll the warm crescents in the powdered sugar mixture.** Allow the Vanilla Crescent Cookies to “ripen” for at least 4-5 days in a tin with real vanilla beans (sliced open lengthwise or use a couple from your vanilla extract). The longer they sit the better! This allows them to get extra tender.