Preheat oven to 400°. In a large bowl, beat butter and 1/2 cup confectioners' sugar until blended. Beat in egg yolk and vanilla. In another bowl, whisk flour and baking powder; gradually stir into creamed mixture until blended (mixture will be crumbly). Shape heaping tablespoons of dough into crescents. Place 1 in. apart on ungreased baking sheets. Bake 12-15 minutes or until edges are lightly browned. Remove from pans to wire racks to cool 15 minutes.
Place remaining sugar in a small bowl. Toss slightly cooled cookies in sugar; return cookies to wire rack to cool completely. Toss cookies in sugar once more before serving. Store in an airtight container, adding any remaining confectioners' sugar to cover cookies.
Every editorial product is independently selected, though we may be compensated or receive an affiliate commission if you buy something through our links.