How do I make a white sauce?

A white sauce is flour cooked in fat and then let down with liquid. Every problem people have with it — lumps, floury taste, thin sauce — comes from one of three things: adding liquid too fast, not cooking the flour, or the wrong ratio.

What you'll need

• Butter
• Plain flour
• Milk
• Whisk
• Heavy saucepan
• Bay leaf (optional)

Step by step

1. Warm the milk gently in a separate pan or the microwave.Warm milk incorporates far more smoothly than cold. This alone prevents most lumps.
2. Melt the butter over medium-low heat.Do not let it brown unless you want a nutty flavour.
3. Stir in an equal weight of plain flour and cook for two minutes, stirring.This is the roux. Cooking it removes the raw flour taste, which is the most common fault in home white sauce.
4. Add the warm milk a splash at a time, whisking each addition in fully before adding more.The first few additions should form a thick paste. Patience here is the whole technique.
5. Once about a third of the milk is in, add the rest more quickly, still whisking.By now the mixture is loose enough to accept liquid without lumping.
6. Bring to a gentle simmer and cook for five minutes, stirring.It thickens as it approaches simmering point. Five minutes cooks out any remaining flouriness.
7. Season with salt, pepper and a scrape of nutmeg.Nutmeg is traditional in béchamel and makes a real difference.
8. For cheese sauce, take it off the heat before stirring in grated cheese.Boiling after adding cheese makes it grainy and can split it.

Tips

• If it goes lumpy, a stick blender rescues it in seconds. Pass it through a sieve if you have no blender.
• Infusing the milk first with a bay leaf, a slice of onion and a few peppercorns, then straining it, makes a noticeably better sauce for very little effort.
• Ratios: 25g each of butter and flour to 500ml milk for pouring, 50g each for a thick sauce that will set in a lasagne.

Common mistakes

• Adding the milk all at once — The flour cannot disperse and you get lumps that are hard to remove.
• Not cooking the roux — The sauce tastes of raw flour, which no amount of seasoning fixes.
• Boiling the sauce after adding cheese — The cheese proteins tighten and the sauce goes grainy or splits.

Questions people ask