1Heat oven to 350°F. Grease bottom of 9-inch square pan with shortening or cooking spray.
2Make cake batter as directed on box, beating all ingredients except apples in large bowl with electric mixer on medium speed 2 minutes. Stir in apples. Spread in pan.
3Bake 40 to 45 minutes or until toothpick inserted in the center comes out clean. Cut into 16 squares.