Note: Creamed spinach can be made 1 day ahead and cooled completely, uncovered, then chilled, covered. Reheat over medium-low heat, thinning with additional milk or water if desired.
- 2 1/2 pounds baby spinach
- Salt, for cooking spinach
- 2 cups whole milk
- 1 small onion, chopped finely
- 1/2 stick unsalted butter
- 3 tablespoons all-purpose flour
- 1/4 teaspoon nutmeg, freshly grated
- 1/4 teaspoon salt, or to taste
- 1/4 teaspoon pepper, or to taste
Cook the spinach in 2 batches in 1 inch of well-salted boiling water in an 8-quart pot, stirring constantly, until wilted and tender, 1-2 minutes. Drain in a colander and rinse under cold running water until cool. Squeeze small handfuls of spinach to remove as much moisture as possible, then coarsely chop.
Heat the milk in a small saucepan over medium heat, stirring, until warm. Meanwhile, cook the onion in the butter in a 3-quart heavy saucepan over medium-low heat, stirring occasionally, until softened, about 4 minutes. Whisk in the flour and cook the roux, whisking, 3 minutes. Add the warmed milk in a fast stream, whisking to prevent lumps, then simmer, whisking, 3-4 minutes (mixture will be thick). Stir in the nutmeg, spinach, ¼ teaspoon of salt, and ¼ teaspoon of pepper, or to taste. Cook, stirring, until hot.