Bechamel sauce can be used in a variety of homecooked dishes, including lasagne, pies and pasta bakes.
Melt the butter in a saucepan over medium heat.
Add the flour and stir with a wooden spoon until the mixture is light blond in colour and when a slightly nutty aroma develops. This paste is called a roux. Cook out the paste for 3-5 minutes, ensuring the roux does not burn.
Whilst stirring, add the milk gradually until fully incorporated into the roux. If the mixture goes lumpy, take the sauce off the heat, keep stirring, making sure you are catching the bottom of the pan.
Bring to a simmer, then reduce the heat to low. The mixture will then thicken.
Whisk in the grated cheese if you are using at this point. Mix until the cheese is fully incorporated.