This is a ridiculously simple recipe that I picked up from a friend, and I made it as the birthday cake for Jeff this year. It was very tasty, and well-received...you'll look REALLY capable if you make this one! :)
carton of ice cream of choice
box of cake mix of choice (and the stuff to make it)
buttercream icing (net post)
Put the ice cream in a bowl and let it completely thaw -- as in, soup. Line the pan you will use to bake the cake in with wax paper. (I used saran wrap, and it was REALLY hard to get the saran wrap off after the ice cream re-froze. I haven't actually tried the wax paper, but I hear it's what you're actually supposed to have.) Pour the ice cream into the pan and spread it flat. Re-freeze the ice cream.
Lift the ice cream layer out of the pan by the wax paper, and put it back in the freezer. Make the cake mix as directed, baking it in two layers. When the layers have totally cooled, remove them from the pans and freeze them on wax paper.
When everything is totally frozen, stack the cakes and ice cream in layers. (I used a paper plate as a base and toothpicks to hold it all together.) Put the entire thing back in the freezer to get nice and solid.
Make the buttercream icing. Frost the cake, then allow the icing to freeze.
Mix up the colored icing you want, decorate the cake, then (you guessed it) refreeze.
This cake takes about 2 full days to make just because of all the freezing, so plan accordingly. Also, it ends up being very tall (3X the height of one of your cake pans), so make sure you have freezer space! Last thing...if putting in candles, be aware that they might be hard to get through the icing layer.