Thankfully, I saved quite a bit of investment in both money and space, as these turned out beautifully even without the dedicated popover pans. (Though they did make quite a bit of a mess of my muffin tins!) In fact, these barely lasted the hour, much less the day ... it was one of the rare hits that every single person in the household craved, and they're so light and airy that no one felt too guilty about scarfing down multiples in one sitting.
- Grind porcini to a powder in an electric coffee/spice grinder or a blender (you’ll have about 1/4 cup). Whisk together porcini powder, flour, salt, eggs, milk, and melted butter until smooth, then let rest, chilled, 1 hour.
- Preheat oven to 400°F with rack in middle. Butter popover cups. Cut remaining 2 Tbsp butter into 12 pieces.
- Heat popover pans in oven 2 minutes. Remove from oven and add a piece of butter to each cup. Return to oven and heat until butter is bubbling, about 1 minute. Divide batter among cups (a scant 1/2 cup each) and bake until puffed and golden-brown, 30 to 35 minutes.
- Pierce top of each popover with a sharp knife to release steam, then continue to bake until deep golden-brown, 5 to 10 minutes more. Serve immediately.
Popovers can be baked 4 hours ahead. Remove from pans and reheat on a baking sheet in a 350°F oven until hot and crisp.