1. In a bowl, with an electric mixer on medium speed, or in a food processor, beat or whirl butter, 1/3 cup powdered sugar, the vanilla, the flour, 1/2 teaspoon cinnamon, and the baking powder until smooth and well blended. Stir in hazelnuts.
2. Shape dough into 3/4-inch balls and, using your fingers, roll each into a 1 1/2-inch rope tapered to points at ends. On buttered or cooking parchment-lined 12- by 15-inch baking sheets, form each rope into a crescent.
3. Bake cookies in a 300° oven until pale golden, 20 to 25 minutes; if baking more than one pan at a time, switch pan positions halfway through baking. Let cool on sheets for 5 minutes.
4. In a shallow bowl, mix remaining 1 1/3 cups powdered sugar with remaining 2 teaspoons cinnamon. Gently turn warm cookies in powdered sugar mixture, a few at a time, then set on racks to cool. When cool, coat cookies again with powdered sugar mixture.
Note: Nutritional analysis is per cookie.