4yellow-fleshed potatoes, such as Yukon gold (about 12 ounces)
1/2cupfinely chopped onion
1tablespooncornstarch
1/2teaspoonsalt
1/4teaspoonpepper
Two 5-ounce containers baby spinach
8ouncesmushrooms, sliced
3ouncesSwiss cheese, shredded
2tablespoonsParmesan cheese
2large eggs
2large egg whites
2/3cupmilk
1/2teaspoonkosher salt
1/4teaspoonground pepper
1/4teaspoonnutmeg
Instructions
Preheat the oven to 400°. Grease a 9-inch glass pie dish with 1 tablespoon butter. Using a food processor fitted with a shredding attachment, shred the potatoes; transfer to a large bowl and stir in the onion, cornstarch, 1/2 teaspoon salt and 1/4 teaspoon pepper.
In a large skillet, heat 1 tablespoon butter over medium heat. Add the potato mixture, flattening it into a 10-inch layer, and cook until the bottom is golden, about 10 minutes. Loosen, then invert onto the pie dish (brown side up) and mold into a crust. Bake about 20 minutes.
Meanwhile, preheat the skillet over high heat. Add the spinach and 1/4 cup water and cook, stirring, until wilted; drain; set aside. Once cool, squeeze out any excess water with hands and then wrap in paper towels and squeeze again. Chop the spinach.
In the same skillet, heat the remaining 1 tablespoon butter over medium heat. Add the mushrooms and cook, stirring occasionally, until browned, about 10 minutes. Add the spinach; season with salt. Spoon half of the spinach mixture into the crust, add the Swiss and Parmesan cheese, then top with the remaining spinach mixture.
In a bowl, whisk together the eggs, egg whites, milk, 1/4 teaspoon salt and 1/4 teaspoon pepper and nutmeg. Pour into the pie dish and bake until set, 20 to 25 minutes. Let cool 20 minutes before serving.