Ingredients

• 3 lb baby spinach
• 1 1/4 cups whole milk
• 1 cup heavy cream
• 1 small onion, finely chopped
• 1/2 stick (1/4 cup) unsalted butter
• 1/4 cup all-purpose flour
• 1/8 teaspoon freshly grated nutmeg

Instructions

1. Cook spinach in 2 batches in 1 inch of boiling salted water in an 8-quart pot, stirring constantly, until wilted, 1 to 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.
2. Heat milk and cream in a small saucepan over moderate heat, stirring, until warm. Meanwhile, cook onion in butter in a 3-quart heavy saucepan over moderately low heat, stirring occasionally, until softened, about 4 minutes. Whisk in flour and cook roux, whisking, 3 minutes. Add warm milk mixture in a fast stream, whisking constantly to prevent lumps, and simmer, whisking, until thickened, 3 to 4 minutes. Stir in nutmeg, spinach, and salt and pepper to taste and cook, stirring, until heated through.