This is simple and easy. It tastes good as well and the varieties are endless. This is what you will need:
-1 box of cake mix (any flavor you like)
-Ice cream (again any flavor--size depends on how big your cake is. I usually buy just the 1/2 gallon)
-Frosting (any kind you like)
Cook the cake mix according to directions on the box (I usually do the 2, 9 in. cake pan size, but it is up to you)
Let the cake cool and soften the ice cream while you wait (just sit it out)
Take one layer of cake and start putting the ice cream onto the layer, molding it to the layer of cake (you could always melt the ice cream to the shape you want and then refreeze I suppose). Do this quickly then put on the top layer. Let it freeze for about 30-60 min depending on how soft your ice cream was when you finished layering it on.
Pull it out of the freezer and then frost it.
Once frozen, you can top with chocolate or decorate any way you like and then refreeze once more. Allow 12-24 hours to freeze before serving to ensure that the middle is not too soft.