The key here is to cook the sauce over a low heat and take your time. Once you have the white sauce you can add cheese and mustard for a cheese sauce, mushroom and cooked onions for a mushroom sauce, and so on.

Using a non-stick pan and a wooden spoon with a corner (to enable you to get into the edges of the pan) melt one ounce of butter. Stir in one ounce of flour, making a smooth paste. Cook for one minute over a low heat until this paste - known as a roux - becomes a light golden brown.

Add three quarters of a pint of milk a little at a time, stirring or whisking continuously - this will ensure that lumps do not form. Continue cooking over a low heat and stirring right into the corners of the pan while you do this, until all of the milk has been added. Cook for a minute or so longer to thicken, then remove from the heat and add any more ingredients. Why not try crumbling some blue cheese in with a pinch of cayenne pepper?