In a small bowl, mix together the all-purpose flour, hazelnut flour and salt. Beat the butter and granulated sugar with an electric mixer on medium-high speed until creamy. Split the vanilla bean, scrape out the seeds using the back of a thin knife and add to the butter with the egg yolk. Beat until combined. Gradually mix in the flour mixture until just combined.
Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper.
Cut the log into 18 pieces and roll each piece into a crescent shape. Put the crescents on the lined baking sheets, about 1 inch apart. Bake until the cookies are set and the bottoms and edges are browned, about 14 minutes. Cool on the baking sheets for a few minutes. Dust with confectioners' sugar while warm, and then transfer to a wire rack to cool completely.
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