Pour the milk into a medium saucepan and place it over a medium heat for 7 minutes, until warmed through. Set aside.
Place a second, smallish saucepan over a low–medium heat. Add the butter and allow it to melt. Then, using a spatula or wooden spoon, gradually beat in the flour, about a tablespoon at a time, until you have a thick paste. You don’t want the paste to start browning – if you’re worried just take the pan off the heat to slow things down a little as you add.
Once all the flour is in, cook, stirring, until you have a dough-like consistency and the paste is coming away from the sides of the pan.
Little by little, add the warmed milk, making sure you allow the first addition to fully incorporate into the paste before adding more. Keep mixing to avoid lumps – switch to a whisk if you need to.
Once all the milk is in and you have a smooth, thick sauce, season with the salt and nutmeg.
Now, simply add your cheese and stir to melt in and combine for the perfect cheesy sauce! If you’re not using the sauce straight away, transfer it to an airtight container (leave it to cool before you put the lid on).
