Make the vanilla confectioners' sugar

Cup of Yum
1. In an airtight container, combine the confectioners' sugar and vanilla bean and let stand, covered, for at least 24 hours. Sift before using. (The vanilla sugar will keep in an airtight container at room temperature for up to several months.)

Make and bake the Viennese vanilla crescent cookies

1. In a food processor or high-powered blender, pulse together the flour, 1/4 cup confectioners' sugar, salt, and hazelnuts until the nuts are finely ground, about 30 seconds. Add the butter and pulse just until a dough forms. If the dough is crumbly, you may need to pulse it a little longer until it forms a dough. Turn the dough onto your work surface and gently form it into a ball and then flatten it into a disk. Wrap it in plastic wrap or wax paper and refrigerate for at least 2 hours and up to 24 hours.
2. Preheat the oven to 350°F (175°C). Adjust the oven rack to the center of the oven.
3. Roll level tablespoons of dough (about 18 grams) into balls. Then roll each ball on a smooth surface into a 3-inch log with slightly tapered ends. Bend each log to form crescents and arrange them about 1 inch apart on baking sheets. ☞ TESTER TIP: If you tend to have hot hands, try occasionally cupping a few ice cubes in your palm while working with the dough. It actually helps keep the butter from starting to soften, which in turn helps your cookies retain their shape.
4. Bake the cookies until the edges are pale golden, 12 to 15 minutes.
5. Transfer to a wire rack to cool slightly, about 2 minutes.

Coat the Viennese crescent cookies

1. Sift enough vanilla confectioners' sugar onto a rimmed baking sheet to cover the bottom.
2. Carefully transfer the slightly cooled baked crescent cookies to the sugared baking sheet and sprinkle with enough sugar to coat completely. Move the crescents to wire racks to cool completely. (The cookies keep, layered between sheets of wax or parchment paper, in an airtight container at room temperature for up to 5 days.)