Preheat oven to 325 In food processor with knife blade attached pulse pecans with 14 cup confectioners sugar until nuts are very finely ground Add butter and vanilla and process until smooth occasionally stopping processor and scraping side with rubber spatula Add flour process until evenly mixed and dough forms With floured hands shape dough by rounded teaspoonfuls into 34-inch balls Place balls 1-inch apart on ungreased large cookie sheet Bake 16 to 18
minutes or until bottoms are lightly browned and cookies are light golden Transfer cookies to wire rack cool slightly about 3 minutes