These little loaves turned out to win my desire like no bread has in quite some time. But they are fussy. The most common snag is the collapse. While I can't claim to have the most robust preparation nor a systematic experimental design, I think I have a few critical parameters ironed out:
1. Ingredients should be at room temperature. I went to the extreme on this. I blended the ingredients (eggs 100 g, flour 135 g, salt 5 g, milk 240 g, butter melted 12 g ==> 8-10 popovers) with an immersion blender, poured the batter into an empty soda bottle and let it sit out overnight. A few minutes before dispensing, I gave it a shake.
2. Baking temperature. I went nuts on this. I tried a bunch of dual temp modes and still feel it's unnecessary. Currently I'm at a constant 425°F in a preheated oven for 30 minutes; I might move to 400°F for a final run.
3. Baking time. Bake LONG enough. The collapsing popover is inevitable if it's not just shy of being burnt. This is another reason I'll go with a longer time and lower temp, the popover structure is delicate until fully cooled. But, 425°F worked well and it's where I'll hang my hat a while.
4. The pan. Despite my spiffy clean aluminum pans, popovers still stuck and the death knell of the popover puffiness is a tug to get it out of the pan. I bought a Chicago Metallic mini popover pan, (don't worry, the mini is the equivalent of a standard 2.5/3.0" cupcake pod's volume) and the popovers almost leap from the pan - no sticking at all. Worth the investment.
5. To preheat or not. Preheating the pan is common but not always done (Alton Brown doesn't preheat, Ina Gartner preheats exactly two minutes, ...). A more reliable starting point is room temp, with each cup lubed with a ca. 1 teaspoon of vegetable oil.
That's the current state of popovers in our kitchen. A few more runs and I'll be ready to try some nifty additions: cheese, bacon, etc.