Is there a non-penetrative method for checking cake doneness?
If the reason you don't want to use a toothpick is that it leaves a big hole, you can buy a cheap little item called a cake tester that is just a thin piece of wire with a little handle. It leaves such a small hole that as to be unnoticeable. As a bonus, it is quite useful for checking the doneness of vegetables. This is the one I use.