In a large bowl, cream butter and confectioners' sugar until light and fluffy. Beat in vanilla. Combine flour and salt; gradually add to creamed mixture and mix well. Stir in pecans. Refrigerate until chilled., Preheat oven to 350°. Roll into 1-in. balls and place on ungreased baking sheets. Bake 10-12 minutes or until set. Roll warm cookies in additional confectioners' sugar; cool completely on wire racks. Roll cooled cookies again in confectioners' sugar.