The story ended happily, but not as expected.
To tell the truth, they weren't plain brownies. I'd had the idea of making reverse-s'mores brownies, so there was a layer of graham crackers at the bottom and a layer of marshmallows on those. I poured the batter over the whole thing.
I think maybe the crackers acted as an insulator, slowing the baking process. I gave the pan another 10 minutes at 400 yesterday, but they didn't firm up much.
The good part was that nobody complained, and the warm brownies were eaten by everyone. Some called them "pudding-like" -- anyway, it was a fun experiment.