60g butter
1/3 cup plain flour
2 cups milk
Melt butter in pan, heat until bubbly. Add flour all at once, stir quickly over heat with a wooden spoon until smooth. This should take only a few seconds. Continue stirring until mixture bubbles again, boil for about 30 seconds, stirring constantly; do not allow to burn.
Gradually stir in milk over heat, continue stirring over medium heat until Sauce boils and thickens. Reduce heat, simmer, stirring for further 30 seconds.
Makes about 2 cups.