I'm making my first topsy turvy cake, and I could use some good recipe suggestions for a sturdy cake that would still be tasty (taste is actually the #1 concern for the client, above appearance). She would like marble cake, but any other suggestions would be great--since she seems to think cake only comes in white, chocolate and marble, haha. What filling would you recommend for such a cake? I don't want one that would be too soft and cause the cake to shift at all (even with support from dowels). I don't want to take any chances by compromising the structure, but I know it just has to taste good!

Thanks so much!