Melt butter in a saucepan over medium heat.
Add flour. Cook, stirring, with a wooden spoon, for 1 to 2 minutes or until mixture bubbles.
Gradually stir in milk.
Bring to the boil.
Reduce heat to medium.
Cook, stirring, for 4 to 5 minutes or until mixture thickens.
Season with salt and pepper.
Allow to cool before refrigerating.