Mix the flour very smoothly with a little water.
Put the rest of the water, with the milk and butter, in a saucepan on the fire to boil.
When it boils, put in the flour, stirring until the sauce is cooked.
Add pepper and salt to taste. If liked, a few drops of lemon juice or vinegar may be added.
This sauce will form the basis of many other plain sauces: To use with fish, put in a tablespoonful of anchovy. Onion sauce is made by adding cooked and chopped onions when the sauce is ready. Caper sauce, by adding capers; or, as a substitute, chopped gherkin.
This sauce may be made still more economically by using water only instead of milk.