Melt the butter in a pan.
Add an equal quantity of plain flour and cook for 5-10 minutes until it has a sandy consistency, creating a roux.
Heat the milk in a separate pan, but do not boil it.
Add the hot milk to the roux a little at a time, whisking to incorporate it and create a smooth béchamel sauce.
Season with salt.
To make a mornay sauce, add grated gruyère and cheddar cheese to the béchamel and stir until melted and incorporated.
To make a sub sauce, sauté onions, then blend them with the béchamel.
To make a mustard sauce, add mustard and tarragon to the béchamel.
To make a sauce aurora, mix béchamel with tomato purée.
To make a horseradish sauce, add grated horseradish, creamed horseradish, black pepper, and vinegar to the béchamel.
To make a parsley sauce, add lemon juice and chopped parsley to the béchamel.
