2 tablespoons unsalted butter
½ cup finely chopped onion
8 ounces white button mushrooms, wiped clean, stemmed and thinly sliced
About 10, 2-inch-wide (4 ounces total) shiitake mushrooms, stemmed and minced
1 teaspoon minced or crushed garlic
1 teaspoon sea salt
½ teaspoon dried thyme
Freshly ground black pepper
3 large eggs, preferably at room temperature
1 cup low-fat milk
1 cup unbleached all-purpose flour
Heat the oven to 375 degrees with a rack in the center position.
Melt 1 tablespoon of the butter in a 9- or 10-inch cast-iron skillet over medium-low heat. Add the onion and cook, stirring, until it softens, about 5 minutes. Add the mushrooms, garlic, ¾ teaspoon salt, the thyme and a generous amount of pepper; cook, stirring often, for about 15 minutes or until the mushrooms' liquid has been released and has evaporated in the skillet and the mushrooms start to turn golden around the edges. (It will seem like a lot of mushrooms at first, but they will cook down.) Remove from the heat.
Meanwhile, combine the eggs, milk, flour and the remaining ¼ teaspoon salt in a blender; purée to form a smooth, aerated batter. (Alternatively, if you don't have a blender, whisk the ingredients together in a medium bowl. It's fine if the mixture has a few lumps.)
Transfer the mushroom-onion mixture to a bowl. Rinse and dry the skillet, then return it to the stove top over low heat. Add the remaining tablespoon of butter; once it has melted and begun to foam, immediately remove from the heat and swirl to coat to the skillet. (Be sure the edges of the skillet are coated; this will ease removal after the popover is baked.) Add the mushroom-onion mixture, spreading it into a fairly even layer, then pour in the batter.
Transfer to the oven and bake 25-30 minutes or until the batter is dry on top and feels solid when touched lightly with a fingertip. The popover will be slightly puffed (it deflates fairly quickly), and its edges will have shrunk from the sides of the skillet and become quite brown. Cut into wedges and serve hot or warm.
Serves three to four.
Cook's notes: For the deepest flavor, use a combination of white and shiitake mushrooms, but you can substitute cremini or wild mushrooms for part or all of the mix.
Nutrition values per serving (assumes 4): 280 calories, 11 g fat (6 g saturated fat), 32 g carbohydrates, 2 g dietary fiber, 3 g sugar 13 g protein, 180 mg cholesterol, 620 mg sodium.
"The Heart of the Plate: Vegetarian Recipes for a New Generation" by Mollie Katzen (2013 Houghton Mifflin Harcourt)