Lumps also happen when you don’t continuously whisk the sauce and it cooks unevenly and thickens on the base of the pan before you can blend it into the rest of the mixture. The outside of the little nuggets of dried flour then turn to gel in the sauce as it boils, trapping the rest of the flour inside and forming a hard lump. Usually, it begins when milk has been added too quickly and not been beaten in sufficiently, so the flour hasn’t blended fully with the liquid. Whisk in 50g (2oz) - 100g (3½oz) (depending on how cheesy you like it) of finely grated gruyere or mature cheddar until the cheese has melted and combined with the sauce. Remove the sauce from the heat, grate over some nutmeg, and add a large pinch of cayenne pepper and/or mustard powder.Simmer the sauce for at least 2min, until thickened and glossy, whisking all the time as the sauce bubbles.

Once all the milk is incorporated, put the pan back on the heat and bring to boil, whisking continuously and making sure to scrape right into the corners of the pan.

You can whisk slightly larger amounts of milk once the sauce looks liquidy instead of pasty. Whisk the milk into it a tiny bit at a time, making sure the milk is fully incorporated before adding the next splash.

Strain the infused milk into a jug (or measure plain, cold milk into a jug).

Bubble the roux for 1min, whisking continuously.Melt 15g (1/2oz) butter in a pan over a medium heat, then stir in 15g (1/2oz) plain flour to make it thicker.You can skip this step and use the same amount of plain, cold milk in step 4, if you are short of time. Bring to just under the boil then remove from the heat and leaf to infuse for 20min. If you want to infuse your milk to give it real depth, put 300ml (1/2 pint) milk in a pan with ¼ onion, 1 bay leaf and 6 peppercorns.Or, you can use it as a nacho cheese sauce, just don’t add the nutmeg. The recipe below makes an approximate 400ml (12fl oz) quantity of cheese sauce, which is enough to coat 150g (5oz) pasta (dried weight) to serve 2 people. The steps are mostly the same as making a white or bechamel sauce.

Cheese sauce with roux