The cake decorators at the blog Once Upon A Pedestal are known for their amazing designs. This one in particular uses white cake mix, a little food coloring (though you could use natural if you're opposed) and a two-step process to get the look above. Although they use a cake pop maker, you can make your own, but the rest of the process should be easy!
Get The Recipe: Polka Dot Cake from Once Upon A Pedestal
(Image: Once Upon A Pedestal)