Easy and quick white sauce best with fish

Ingredients
400ml milk
20gram floor
40grams butter
Method

When you're ready to make the sauce, put the milk in a saucepan, then simply add the flour and butter and bring everything gradually up to simmering point, whisking continuously with a balloon whisk, until the sauce has thickened and becomes smooth and glossy.
Then turn the heat down to its lowest possible setting and let the sauce cook very gently for 5 minutes, stirring from time to time season to taste . Add parsley to the top after poring over your dish great with white fish.