Is there some way to check a cake is done without using a toothpick or other penetrative device?
I like the thermometer idea, but no one seems to know how the heck to use them.
http://www.baking911.com/cakes/data.htm I found some baking times for specific sized cakes. For me, I just use the toothpick method.
If it's a spongecake, you can check by pressing down on it and if it "bounces" back it's done.
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.
Touch the center with the your finger. Texture will tell. It should have some spring back and not be gooey or too jiggly. If the center is cooked, so is the rest.
As for overcooking, I use the edges as a guide. If they're starting to brown, (either the over temp is just too high), or the center is probably done too.
Finally, smell. Fresh cake will have a sweetness. Underdone will still be a bit 'doughy'. Overcooked will start to have bready/crusty/burnt overtones.
Use a digital thermometer.
Finding correct core temperatures is a bit tricky though.
Update: Corriher suggests 98 degrees Celsius in her book BakeWise.
I always wiggle the cake a bit to see if the top moves. If it is undone the top with wiggle like it's wet. If done, it should be firm. If you know your oven well, the timing should be a good estimate too, and then use the wiggle method.
Depending on the cake you are baking you can also listen to it. Some cakes have a slight bubbling sound while undone.
Simply use a fork.
poke a wooden toothpick into the center of a cake; if it comes out with wet batter, keep cooking; if it comes out clean and dry, contrary to common knowledge, it's probably overcooked; if it comes out with a few crumbs stuck to it, it's probably perfect.