16 ounces fresh baby spinach or 1 (12-ounce) bag thawed frozen leaf spinach
2 tablespoons unsalted butter
1 onion, preferably Vidalia, finely chopped
6 ounces mixed mushrooms (such as cremini, chanterelle, morel, shitakes, white button) thinly sliced
1 clove garlic, very finely chopped
1/3 cup heavy cream
1/8 teaspoon freshly grated nutmeg
Coarse salt and freshly ground black pepper
4 large eggs
2 tablespoons finely grated Parmigiano-Reggiano chees (? ounce)
1. Position the oven rack in the upper third of the oven and preheat to 450 degrees. Prepare an ice-water bath by filling a large bowl with ice and water.
2. To cook the fresh spinach, heat 1/2 inch water in a large skillet over high heat. Add half the spinach and cook until wilted, about 30 seconds. Add the remaining spinach cover, and cook, over medium-high heat until tender, about 60 seconds. Drain well in a colander, then set the colander with spinach in the ice-water bath to set the color and stop the cooking, making sure the spinach is submerged. Remove the colander with spinach to drain. Working with a handful at a time, squeeze the freshly cooked, or thawed frozen, spinach between two dinner plates or by hand to remove any excess liquid. Set aside.
3. In the same skillet, heat the butter over medium heat. Add the onion and cook until translucent, 3 to 5 minutes. Increase the heat to medium-high, add the mushroom, and cook, stirring occasionally, until softened and any liquid is released, about 4 minutes. Add the garlic and cook until fragrant, 45 to 60 seconds. Add the cream, nutmeg, and spinach. Season with salt and pepper and bring to a simmer. Remove the pan from the heat.
4. Using the back of a spoon, make 4 nests in the spinach-cream mixture in the skillet. Break an egg into each indentation. Season the egss with salt and pepper and sprinkle with the cheese. Bake until the whites are set and the yolks are still runny, about 8 minutes. Serve immediately.