PREPARE and bake cake mix according to package directions for 13x9-inch cake using the oil, water and eggs. While cake is baking, prepare topping.
COMBINE sweetened condensed milk, cream, evaporated milk and vanilla in large bowl. Slowly whisk in cocoa and cinnamon. Whisk until cocoa is blended into milk.
REMOVE cake from oven. Cool 10 minutes. Using a meat fork or skewer, pierce surface of cake several dozen times. While cake is still warm, pour half the milk mixture over top. Let soak for one minute. Pour remainder over cake. Cover. Chill 1 hour. Spread with whipped topping. Sprinkle with chocolate decors.