In a small pot heat the milk to just hot. Do not boil. Remove from heat and keep warm.
Start the Roux
In another saucepan melt the butter until fully melted and begins to bubble.
Add the flour to the butter (with a whisk) incorporate until thoroughly mixed. Cook this mixture gently for about 1 minute. Do not brown.
Next, add the measured milk in thirds while whisking until all the milk is incorporated. The sauce should come together quickly (2-3 minutes), adjust with extra milk if the sauce is too thick.
Finally, add the salt, ground white pepper, and freshly grated nutmeg. Whisk in and remove from heat. Use as desired.