I am a newbie and haven't cooked anything but the standard 8 in. rounds so far, so how much longer should I allow for a 12in. square...wasc recipe...and do I need a heating core or anything to make sure it cooks evenly? I already use the baking strips.
I would use a flower nail. And set the timer on your 325 oven for 30 mins or so and go from there, testing with a toothpick. I'm sure everyone would do it a little differently, but that is where I would start. GL!
I always rotate my cake pans after 10-11 minutes, no matter what size/shape, because my oven has hot spots. Then depending on the size, I check/rotate again after 10-11 more minutes, then again after 5 mins, and toward the end, every 2 mins. I just bake it till it's "done" however long it takes. Every oven is different. And I have never followed box mix baking times.