Preheat oven to 350º. Butter and lightly flour 9x13 inch baking pan. Sift SWANS DOWN Cake Flour, then lightly spoon into measuring cup for 2 cups. For Cake: Cream butter and gradually add 1 ½cups sugar, eggs and vanilla extract, beating well after each addition. In another bowl, mix SWANS DOWN Cake Flour, baking powder and baking soda. Add flour mixture alternately with sour cream to creamed mixture. For Topping: Mix remaining sugars and cinnamon. Pour half of the batter in prepared pan. Sprinkle walnuts and half of topping on top of batter. Add remaining batter and sprinkle remaining topping on top. Bake approx. 45 minutes or when tester inserted comes out clean. Serve warm.