[Family note: This is sort of like a savory, mushroom-rich Dutch pancake :-).]
2 T. butter
1/2 medium onion (trimmed and peeled)
8 oz. (white) mushrooms (washed, trimmed, and sliced)
8 oz. portobello mushrooms (washed, trimmed, and sliced)
1/4 t. garlic powder
freshly ground black pepper
1/2 t. dried thyme leaves (not powdered thyme)
1 C. milk
1/2 t. salt
1 C. flour
1 T. romano cheese
Find a large (~10″) omelet pan. Add 1 T. butter to the pan and turn the heat to just below medium.
Find a cutting board, a sharp knife, and a colander.
Trim and peel the onion. Mince half the onion. (Save the other half for another recipe.) Add the minced onion to the melted butter. Stir occasionally with a silicone scraper.
Meanwhile, wash the portobellos in the colander, rubbing any dirt off under running water. Trim the woody ends and slice the mushrooms. When the onions are just starting to turn brown along the edges, add the portobellos. Turn the heat up to medium. Stir the mushrooms and onions occasionally with a silicone scraper.
Wash the (white) mushrooms in the colander, rubbing any dirt off under running water. Trim the woody ends and slice the mushrooms. When the portobellos appear to be somewhat cooked, add the (white) mushrooms. Stir.
While the mushrooms are cooking, sprinkle with garlic powder and grind in a bit of black pepper. Stir well. The mushrooms need to cook until they have lost their liquid and that liquid has cooked off, leaving the mushrooms fairly dry and browning along the edges.
Meanwhile, find a cheese grater and a (clean) cutting board and grate about 1 T. of romano cheese. [It's fine to substitute parmesan cheese if that's what you have on hand.]
Then find a medium mixing bowl and a whisk. Crack the eggs into the bowl. (Wash your hands.) Whisk well. Add the milk. Whisk. Add the salt. Whisk. Add the flour. Whisk well, until smooth and light.
Preheat the oven to 375◦. (Be sure to first remove anything you store in the oven!)
When the mushrooms are (finally) done, transfer them to a bowl and rinse/wash out the omelet pan. Return the omelet pan to the burner and add the remaining 1 T. butter. When the butter has melted and the foaming has subsided, swirl the melted butter around to coat the bottom and sides of the omelet pan — go up the sides as far as you can without spilling melted butter.
Immediately transfer the batter to the omelet pan. Spoon the mushroom mixture evenly into the batter. Sprinkle the romano cheese on top.
Put the entire omelet pan in the (preheated) oven and bake for 35-40 minutes. Set a timer.
Find a pancake turner and a large dinner plate (large enough to accommodate the pie).
When the timer goes off, the top of the pie should be firm and golden brown. Turn off the oven and, using oven mitts, place the omelet pan on a wood cutting board or an unused burner. Carefully slide the pancake turner under the edges of the pie to loosen it along the sides and bottom. (The butter you swirled around the pan should have done a good job of keeping it from sticking.) Slide the popover pie onto the large dinner plate.
Cut into wedges — four for a main course, six for a side dish — and serve hot or warm.
[Adapted from the "Mushroom Popover Pie" recipe that appeared in The Washington Post, September 2013]