Hi there,
This is how I make my white sauce:-
1 desert spoon butter
2 - 3 desert spoons plain flour
about half pint milk (depending how thick you want it)
and some gound nut meg.
melt the butter and add flour whisking all the time so you dont get lumps over a low heat, cook for a couple of minutes and then gradually add the milk a little at a time and then the nutmeg let it bubble gently for a a couple of minutes stiring all the time, and serve.
You could also add cheese to this to make a cheese sauce.
Hope this helps.