1Heat oven to 350°F. Spray bottom only of 13x9-inch pan with cooking spray.
2In large bowl, beat sugars, buttermilk, oil, vanilla and eggs with electric mixer on low speed 20 to 30 seconds or until blended. Add all remaining ingredients except apples and walnuts; beat on low speed about 1 minute or until blended. Stir in apples and walnuts. Spread batter in pan.
3Bake 40 to 45 minutes or until toothpick inserted in center comes out clean. Cool in pan on cooling rack 1 hour.