Grill Version: This makes a great make-ahead recipe for the grill as well! Just prepare the recipe as written through assembling the mushrooms. Keep refrigerated until ready to grill, and then instead of broiling the mushrooms for the last step, grill them until warmed through and the cheese is melty.
- 1/2 pound cremini or button mushrooms, halved
- 2 large shallots (4 ounces), quartered
- 4 large portobello mushrooms
- 4 tablespoons olive oil, divided
- 1/2 teaspoon salt
- 1/4 teaspoon freshly ground black pepper
- 5 ounces (about 4 cups) baby spinach leaves
- 1 tablespoon water
- 1 teaspoon dried thyme
- 3 tablespoons sour cream
- 1 cup (about 4 ounces) grated Swiss, Gouda, or cheddar cheese
- 2 tablespoons chopped parsley (for garnish)
1 Get your equipment ready: Preheat the oven to 400ºF. Line a rimmed baking sheet with parchment paper. Set a large strainer over a bowl.
2 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 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 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 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 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 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 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.