Warm the milk – In a microwave safe bowl warm the milk to make it room temprature. Keep it warm while preparing the roux.

Make the roux – In a separate medium saucepan, melt the butter over medium heat. Once fully melted, add the flour and whisk constantly for 1-2 minutes until it forms a smooth paste. The mixture should be pale and slightly bubbly but not browned.

Slowly add the milk – Gradually pour in the warm milk, whisking continuously to prevent lumps. Start with a small amount to loosen the roux, then gradually add the rest.

Cook and thicken – Continue whisking and cook over medium-low heat until the sauce thickens, about 5-7 minutes. It should coat the back of a spoon.

Season – Stir in the salt, pepper, and nutmeg. Taste and adjust seasoning as needed.

Use or store – Remove from heat and use immediately, or cover with plastic wrap (touching the surface) to prevent a skin from forming.