Usually I use a yellow cake mix but I've been toying with the idea of some kind of sponge cake which I love. Only it has to be dense enough to support the fruit.
Yes, the cake has to be dense for this. I once made a recipe that was so light it just didn’t work.
There are lots of easy ‘cake-mix’ recipes out there for Pineapple Upside Down Cake; but I’ve found that it’s best from scratch - and the best are the ones done in the cast-iron pan, for the caramelization.