Beat butter at medium speed with an electric mixer until creamy; gradually add sugar, beating well. Add eggs, 1 at a time, beating until blended after each addition. Add next 7 ingredients; stir well.
Spoon into a greased 13- x 9-inch baking dish.
Bake at 350° for 30 to 35 minutes or until a wooden pick inserted in center comes out clean. Cool on a wire rack; cut into squares. Sprinkle with powdered sugar, if desired.