The recipe for the Death by Chocolate Trifle calls for 2 brownie mixes in the large bar pan. My question is, do you put both mixes in at the same time? They don't run over? I made a single mix in the bar pan once and it was so thin, but when I make the warm nutty caramel brownies they're fine, so wasn't sure what happened there, but just wanted to check before I made it this morning for a lunch hour show... TIA!