My granddaughter named this cake and she asks for it every July 4th. I originally found the recipe on Tasty, although they provide it more through instructions than a list of ingredients, and do not include a frosting recipe. I have included my favorite vanilla frosting in the attached recipe. Either way, we love it!
Here is the Tasty link with a great demo: https://www.google.com/amp/s/tasty.co/recipe/marbled-4th-of-july-box-cake