Start by making a roux; that's an equal quantity flour to butter.
Melt 20 grams of butter in a medium saucepan on a medium heat, then stir in one tablespoon of flour.
Cook it very gently, until it just starts to colour (for about a minute).
Remove the roux from the heat and gradually add one cup of milk, stirring between each addition.
This will ensure a smooth sauce with no lumps.
Place back over medium heat; the sauce will soon start to thicken as the starch and water bind.
Keep stirring the sauce til comes to the boil and thickens, then keep boiling for another three minutes.
Season your sauce with a pinch of salt and pepper to taste, before adding some flavouring: grated cheese, chopped herbs or ground spices.
Then it's time to get cooking! Try tasty tuna croquettes, classic lasagne or a gooey gruyere souffle.
Our favourite though? Has to be good old macaroni cheese.