Creamed Spinach Recipe

Name: Creamed Spinach Recipe
Ingredients: 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