PREHEAT oven to 350°F. Beat butter, 1/2 cup of the powdered sugar and the vanilla in large bowl with electric mixer on medium speed until light and fluffy. Gradually add flour and pecans, beating on low speed after each addition until well blended.
SHAPE dough into 1-inch balls. Place, 1-1/2 inches apart, on ungreased baking sheets.
BAKE 14 to 15 min. or until bottoms of cookies are lightly browned. Cool 5 min. on baking sheets. Roll warm cookies in remaining 1/2 cup powdered sugar until evenly coated; place on wire racks. Cool completely. Store in tightly covered container at room temperature.