Melt the butter in a saucepan (medium heat), add the flour and stir with a whisk, let sweat while stirring. Always stir in small amounts of the measured, cold milk, using the whisk to reach the edges of the pot. Stir in all of the milk, bring to the boil and season.
This basic sauce can be varied in many ways:
HERB SAUCE:
Mix in the chopped herbs. Parsley, chives, dill
A splash of lemon juice gives it a special touch.
CHEESESAUCE:
Stir in 1 tablespoon grated spicy cheese or processed cheese.
CURRYSAUCE:
Half of the milk in the basic sauce can be replaced with coconut milk, but does not have to be.
Mix in 1 tablespoon curry powder and some applesauce, possibly a little more cream.
MUSTARD SAUCE:
Stir in 1 tablespoon mustard and 1 tablespoon butter.
If you want the sauce a little creamier, you can add cream, crème fraîche or more butter or use an egg yolk for alloying.