Preparation Whisk flour in heavy medium saucepan to remove any lumps. Gradually add 1 cup milk, whisking until smooth. Add remaining 2 cups milk and nutmeg; whisk over medium heat until mixture thickens and boils, about 4 minutes. Remove from heat. Stir in Parmesan and butter. Season to taste with salt and pepper.
Preparation Whisk flour in heavy medium saucepan to remove any lumps. Gradually add 1 cup milk, whisking until smooth. Add remaining 2 cups milk and nutmeg; whisk over medium heat until mixture thickens and boils, about 4 minutes. Remove from heat. Stir in Parmesan and butter. Season to taste with salt and pepper.