Beat butter, powder sugar and vanilla in a large mixer bowl until creamy. Beat in flour. Stir in pecans. Roll 1 1/2 to 2 teaspoons of dough into crescent-shaped cookies. Put on ungreased cookie sheet. Bake in preheated 325 °F oven for 30 minutes or until lightly brown. Roll hot cookies in additional powder sugar and let cool on a wire rack.