Spinach-Stuffed Portobello Mushrooms

1 . Stage

Get your equipment ready: Preheat the oven to 400°F. Line a rimmed baking sheet with parchment paper. Set a large strainer over a bowl.

2 . Stage

Chop the mushrooms and shallots: Remove the stems from the portobello mushroom caps. With a paring knife, trim the dirty ends of the stems, and discard. Rinse what remains of the stems, and cut them into 1-inch pieces. In a food processor fitted with the metal blade, combine the cremini or button mushrooms, shallots, and portobello mushroom stems. Pulse several times until the mushrooms and shallots are finely chopped. Set aside.

3 . Stage

Bake the mushrooms on their own: Brush both sides of the mushroom caps with 2 tablespoons of the oil, and sprinkle with salt and pepper. Place them on the baking sheet with the gill side down, and bake for 12 to 14 minutes, or until tender but still a little firm. Remove and set aside. There will probably be quite a bit of excess liquid on the pan; reserve it to add to the filling in step 5.

4 . Stage

Cook and drain the spinach: Meanwhile, in a large skillet over medium-high heat, heat 1 tablespoon of oil. Add the spinach and 1 tablespoon of water to the pan. Cook and stir for 3 to 4 minutes, or until the leaves wilt. Transfer them to the strainer and let drain, pressing out most of the liquid with the back of a spoon. Wipe out the skillet with a paper towel.

5 . Stage

Finish the filling: Over medium heat, heat 1 tablespoon of oil in the skillet. Add the chopped mushrooms and shallots and cook for 5 minutes, or until softened. Add the thyme, 1/4 teaspoon salt, 2 pinches of pepper, and any excess liquid that accumulated on the baking sheet while baking the portobellos. Cook and stir until most of the liquid in the pan evaporates. Remove the pan from the heat. Add the drained spinach and sour cream, and stir until combined. Taste and add more salt and pepper if you like.

6 . Stage

Stuff the mushrooms: Turn the mushrooms on the baking sheet so that the gill side is up. Mound a quarter of the filling on top of each mushroom cap. Sprinkle each with a quarter of the cheese.

7 . Stage

Broil the stuffed mushrooms: Set a rack 6 inches from the broiler element, and heat the broiler. Place the mushrooms under the broiler, and broil for 3 to 4 minutes, or until the cheese melts.

8 . Stage

Serve: Sprinkle with chopped parsley, and serve the mushrooms on top of greens dressed lightly in oil and vinegar, or with rice, farro, or the grain of your choice.