Melt the butter in a medium saucepan. Add the flour, stirring to incorporate. Allow the flour and butter to cook for 2 minutes. The mixture will be a little frothy. This removes the raw flour taste.Heat your milk to almost boiling and then add to the flour mixture and whisk vigorously. Turn the heat to medium-high and continue stirring until it comes to a boil. Boil for one to two minutes and the sauce will thicken. Remove from heat and stir in the salt and pepper. At this point you will be ready to add additional flavorings or additions.