Just plain old while sauce?
2 oz butter, melt in a pan gently and don't let it go brwon. Mix in 2 oz flour and heat until it sort of forms a 'ball' in the middle of the pan.....stir it all the time. Gradually add milk, mixing all the time and heat throug, it will thinkecn up a bit as it cooks, add milk to get the desired consistancy.