In a small sauce pot, melt butter over medium heat.
As soon as butter is completely melted, whisk in flour. Let bubble for 1 minute to cook out the floury taste. Do not let the butter turn brown. Stir as needed.
Next, whisk in milk. Bring to a boil then reduce to simmer. Whisk until thickened and smooth.
Add salt and nutmeg (optional) to taste.
Video
Notes
Be careful not to overcook butter or butter + flour mixture as it bubbles. You do not want the butter to form brown bits.