Combine flour, ground walnuts, baking powder and salt in large bowl; set aside.
Beat I Can't Believe It's Not Butter!® Spread until light and fluffy in medium bowl, with electric mixer about 2 minutes. Gradually beat in 1 cup sugar, egg yolk and vanilla with mixer on low, scraping sides occasionally. Gradually beat in flour mixture on low, then beat on medium 30 seconds or until mixture forms a soft dough. Using 1 tablespoon dough for each cookie, shape dough into crescents, about 3 inches long. Arrange crescents, 3 inches apart on ungreased baking sheets.
Bake 14 minutes or until lightly golden around edges. Cool 2 minutes on wire rack; remove cookies from sheets and cool completely. Sprinkle with remaining sugar.