Combine first 9 ingredients in a large bowl; beat at low speed of a mixer for 1 minute. Combine flour and baking powder; gradually add flour mixture to sugar mixture, beating until well-blended (dough will be soft). Turn dough out onto a lightly floured surface; shape dough into 3 (6- x 4-inch) rectangles. Place rectangles on a baking sheet coated with cooking spray; flatten to 3/4-inch thickness. Bake at 375° for 25 minutes. Remove rectangles from baking sheet; cool 10 minutes on a wire rack.
Cut each rectangle diagonally into (3/4-inch) slices.