Melt butter in a medium sauce pan, over a medium heat.

Once butter is melter add flour and stir constantly for approximately 1 to 2 minutes. . The mixture will bubble, so be sure not to brown or burn it.

Stir in the milk, mixing well. Its recommended to use warn milk (a minute or so in the microwave should do the trick).

Stir constantly until mixture begins to thicken.

Add  salt and pepper ...  season to taste.