- 1 tablespoon olive oil, plus more for the baking dish
- 6 shallots, thinly sliced
- kosher salt and black pepper
- 1 cup dry white wine
- 6 large eggs
- 1 cup heavy cream
- 1 cup whole milk
- 1/4 teaspoon grated nutmeg
- 4 10-ounce packages frozen spinach, thawed and squeezed to remove excess moisture
- 8 ounces grated Gruyère (8 ounces)
- 1/2 cup grated Parmesan (2 ounces)
- Heat oven to 400° F. Coat a shallow 2½- to 3-quart baking dish with oil; set aside.
- Heat the oil in a large skillet over medium-high heat. Add the shallots, ½ teaspoon salt, and ¼ teaspoon pepper. Cook, stirring occasionally, until soft, 6 to 8 minutes. Add the wine and simmer until evaporated, 4 to 6 minutes.
- In a large bowl, whisk together the eggs, cream, milk, nutmeg, ½ teaspoon salt, and ¼ teaspoon pepper. Stir in the spinach, shallot mixture, Gruyère, and Parmesan. Transfer to the prepared baking dish.
- Bake until the spinach mixture is bubbling and the top is golden brown, 45 to 55 minutes.