Sift together flour, baking powder, soda, and salt in a small mixing bowl; set aside.
Melt butter in a large saucepan over medium heat. Remove from heat. Add brown sugar, eggs, reserved flour mixture, and chocolate morsels, stirring well after each addition until thoroughly blended.
Pour batter into a lightly greased and floured 15- x 10- x 1-inch jellyroll pan. Bake at 325° for 25 minutes or until a wooden pick inserted in center comes out clean; sprinkle with powdered sugar. Cool completely in pan; cut into 3- x 1- inch bars to serve.