sorry if this is a stupid question but if I need to make 2, 8x2" thick layers and have a 4" thick cake pan...should I fill all the way up with the batter and adjust the time or cook twice, 1/2 filled?

thanks

ACakes rise during baking. If you fill it all the way up you will be left with a really big mess.

Half way; no more than 2/3 full