Ingredient

Cheese sauce

A cheese sauce is a béchamel with cheese stirred into it, and nearly every failure comes from the same instruction being ignored: the cheese goes in off the heat, and the sauce never boils afterwards.

The béchamel

1. Melt butter and stir in an equal weight of plain flour. Cook this roux over a medium heat for a couple of minutes, stirring, until it smells biscuity rather than raw.
2. Take it off the heat and add a little milk, stirring to a smooth thick paste before adding more. The first additions are the ones that decide whether you get lumps.
3. Keep going, loosening gradually, until all the milk is in and the sauce is smooth.
4. Return to a medium heat and bring it to a simmer, stirring constantly. It thickens suddenly.
5. Simmer gently for at least five minutes. This cooks out the flour and completes the starch gelatinisation — under-cooked béchamel tastes pasty.
6. Season with salt, white pepper and a scrape of nutmeg, which is traditional and genuinely improves it.

Adding the cheese

Take the pan off the heat entirely, wait a few seconds, then stir in the grated cheese until it melts. The residual heat is more than enough.

Cheese is protein and fat held in a delicate structure. Heated past about 70°C the proteins tighten and squeeze the fat out, which is what "grainy and oily" means. Once that has happened there is no reliable way back.

So: off the heat, stir until melted, and never return it to the boil. If it has to be reheated, do it gently and stop before it simmers.

Which cheeses melt well

Mature cheddar

The default. Strong enough to taste through the sauce. Grate it finely.

Gruyère or Comté

Melt beautifully and taste better than cheddar in a mornay. The classic choice.

Parmesan

Excellent for savoury depth, but it does not melt smoothly on its own — use it alongside a melting cheese.

Mozzarella

Stringy rather than smooth. Good on top, poor stirred in.

Very aged or very hard cheeses

Low moisture and high protein means they break easily. Use sparingly.

Pre-grated cheese

Coated in starch to stop it clumping, which makes a slightly gritty sauce. Grate your own.

What goes wrong

• Lumpy — milk added too fast at the start. Whisk hard, or blend it, or sieve it. All three work.
• Grainy and oily — the cheese was boiled. Off the heat, always.
• Tastes of flour — the roux or the sauce was not cooked long enough.
• Too thin — simmer longer, or use more roux next time. A rough guide is 50g each of butter and flour to 500ml milk for a coating sauce.
• Skin forming — press cling film onto the surface, or dot the top with butter.
• Splits on reheating — it was overheated once already. A splash of milk and a stick blender usually saves it.

Common questions