Thanks for the tips everybody! They came out great and were a big hit served with butternut squash and apple soup.

The shape is right, heavy is best, and the suggestion to leave empties sounds right. The absolute best pan for popovers is made of cast iron, but they don't seem to be made any more. I've seen them on ebay. If you plan on making them again and have room for another specialty piece of cookware, it's really ideal. You preheat them, so the initial rise makes the outcome superior.

Kim Boyce of Good to the Grain recommends using two 12-cup muffin tins to make 12 muffins, spreading them out, so you get a better rise. That would probably work for popovers, too.

Yes. They won't rise as tall but can be done in a muffin tin. Though would it be more like a dutch baby? I vaguely remember an Alton Brown episode on popovers and he made dutch babies with the same batter, I think.

Yes you can! I leave the center cups empty because the first time I made them in a muffin pan, surrounded by the other popovers they were not as nice as the rest. Maybe a fluke, but I've not done it since.