Preheat the oven to 350°F. Grease and flour two round cake pans and set aside. Grease a 10-cup Bundt pan, a 9" x 13" pan, or two 9" round cake pans. Prepare the cake mix according to the package (I like Duncan Hines Classic Chocolate), substituting root beer for the water. To make the cake: In a large bowl, whisk together the flour, sugars, baking soda, salt, and spices. In a medium saucepan, bring the root beer, butter, and cocoa powder to a boil, stirring occasionally. It may seem hard to believe, but all you need for this 2 ingredient cake recipe is a box of chocolate cake mix and some root beer!. How to Make Root Beer Float Cake: Preheat your oven to 350-degrees. No eggs, no butter, no oil. Then add the vanilla, and beat. This super easy root beer float cake is the latest pop cake recipe the kids and I have made.