Remove large stems from spinach, and rinse with cold water; drain. Place a large Dutch oven over medium heat, and add spinach. (Spinach will need to be tightly packed into the pan to cook all of it in one batch). Cover and cook 5 minutes or until spinach wilts; stir spinach well after 2 minutes. Place spinach in a colander, and drain well, pressing spinach with the back of a spoon to remove as much moisture as possible.
Place pan coated with cooking spray over medium heat until hot. Add shallots; sauté 2 minutes. Combine flour, salt, and nutmeg; add to pan, stirring well. Cook 30 seconds. Add milk and cheese, stirring with a whisk; cook 1 minute or until thick. Add spinach; cook 30 seconds or until thoroughly heated.