Preheat oven to 350°. Cream butter, shortening and sugar until light and fluffy, 5-7 minutes. Beat in egg and vanilla. In another bowl, whisk flour, baking powder and baking soda; gradually beat into creamed mixture., Shape into 1-in. balls. Roll in additional sugar. Place on greased baking sheets; flatten with a glass. Bake until set, 10-12 minutes. Remove to wire racks to cool.