I can't find a boxed mix that will make a 9X13 pan of brownies, only 8X8 or 9X9 - what should I do?
You could just use 2 boxes of those smaller mixes and do them together in the 9X13 pan. Or, if you would prefer, make just one 8X8 or 9X9 pan, and then you will half the recipe for the peanut butter layer and the ganache layer.