I've been making terrifically voluminous popovers for years, using the very simple recipe in Mark Bittman's "How to Cook Everything".
For the past few weeks, they haven't been rising nearly as much, sometimes barely clearing the edge of the muffin tin. I've tried beating the heck out of the batter to incorporate more bubbles, as well as underbeating the batter somewhat, in order (my thinking goes) to keep the strands of protein intact. I've also been careful to preheat the oven and the muffin tin for a long time. No luck.
My two remaining theories are:
1. Lately I've been cutting the recipe in half because a dozen popovers is just too much for the two of us. Could this be throwing off the recipe?
2. It's been extremely rainy this spring. Could humidity be a factor?
Any other ideas?