Melt the butter: In a medium saucepan over medium heat, melt butter until bubbly but not browned.
Make the roux: Add flour and whisk constantly for 1–2 minutes until smooth and slightly golden. This removes the raw flour taste.
Add milk: Slowly pour in milk while whisking to prevent lumps. Keep stirring until the sauce starts to thicken.
Season: Add salt, black pepper, and optional nutmeg. Taste and adjust seasoning.
Optional add-ins: Stir in Parmesan or herbs if using, and cook for another 1–2 minutes until smooth and creamy.
Serve: Pour over pasta, vegetables, or use in casseroles and lasagna immediately.
