01 - Melt the butter in a medium saucepan over medium heat.
02 - Add the flour and whisk continuously for 1-2 minutes to create a smooth roux without browning.
03 - Gradually whisk in the milk to avoid lumps, maintaining constant stirring.
04 - Bring to a gentle simmer, reduce heat to low, and cook while stirring frequently until the sauce thickens, approximately 5 to 7 minutes.
05 - Stir in heavy cream if using, followed by salt, pepper, and nutmeg. Adjust seasoning to taste.
06 - Remove from heat. Use immediately or cover surface with plastic wrap to prevent skin formation if storing.