Preheat oven to 350°. Grease and lightly flour two 9-inch round cake pans*; set aside.
Beat cake mix, Hellmann's® or Best Foods® Real Mayonnaise, water, eggs and cinnamon 30 seconds in large bowl with electric mixer on low speed. Beat on medium speed, scraping sides occasionally, 2 minutes. Pour batter into prepared pans.
Bake 30 minutes or until toothpick inserted in centers comes out clean. Cool on wire rack 10 minutes. Remove cakes from pans and cool completely. Sprinkle, if desired, with confectioners sugar or fill and frost.