1 Preheat oven to 325F (160C).2 Combine all ingredients, except the oil spray and whipped topping in a large bowl. Using an electric mixer, mix according to directions on package.3 Coat a 9 x 13 inch (22 x 33 cm) nonstick cake pan with cooking spray and spoon batter evenly into the pan.4 Bake 25-35 minutes or until wooden pick inserted comes out clean. Place pan on wire rack and cool completely.5 At time of serving, spoon 1 Tbsp (15 mL) of the whipped topping on each slice. Leftover cake can be frozen for up to one month, if desired.