How to Make It
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.