In a large bowl, cream butter and sugar until light and fluffy. Combine the flour, baking powder and salt; gradually add to the creamed mixture and mix well.
Spread into an ungreased 11x7-in. baking pan. Prick several times with a fork. Bake at 350° for 20-22 minutes or until edges begin to brown. Dust with confectioners' sugar. Cool on a wire rack. Cut into bars.