Cheese sauce is useful for cauliflower cheese, lasagne, macaroni cheese and a dozen other dishes. It needs only butter, flour, milk and cheese, yet it can turn into a lumpy paste if the milk goes in too fast or a gritty sauce if the cheese is boiled aggressively.
The reliable method is to make a smooth white sauce first, then melt the cheese into it off the strongest heat. Once you've learned that sequence, you can make it thicker for a bake or looser for pouring.
Ingredients for about half a litre
Use 40g butter, 40g plain flour, 500ml milk and 100–125g mature cheddar, finely grated. Add black or white pepper and a little mustard if liked.
You may not need much salt because the cheese contributes its own. Taste at the end before adding extra.
These quantities are a practical starting point. If you're making macaroni cheese for a large family, scale them up and allow more pan space for whisking.
Choose a suitable saucepan
A medium heavy-based saucepan heats milk more evenly and is less likely to scorch than a very thin one.
Have a whisk, wooden spoon and measured jug of milk ready before switching on the hob. You'll need to stir steadily during the first few minutes.
Use a pan large enough to allow vigorous whisking without splashing hot sauce over the sides. Milk can burn skin, so don't crowd the worktop.
Grate cheese before you start
Fine freshly grated cheddar melts more predictably than large cold chunks. A mature cheddar gives a stronger flavour, allowing you to use a sensible quantity.
Avoid adding huge handfuls of cheese at once. The sauce should be able to absorb each addition before you add the next.
If you're using a processed cheese or a specialist melting blend, follow a recipe designed for it. Cheeses differ in fat, moisture and protein and may behave very differently.
Melt the butter gently
Place the saucepan over medium-low heat and add the butter. Let it melt without browning heavily.
Once liquid, stir in the plain flour. The mixture forms a thick paste known as a roux.
Keep moving it for about one to two minutes. This cooks out some of the raw flour taste but shouldn't burn or become dark brown when you're making a pale cheese sauce.
Add milk in small stages
Pour in a little milk and whisk vigorously. The first addition may turn the paste into a very thick mass, but continue until it becomes smooth.
Add another small splash, whisk it in and repeat. Once the mixture has loosened, you can pour the remaining milk more steadily while whisking.
This gradual technique is the easiest defence against lumps. Dumping a whole cold carton of milk into a pan of roux can leave stubborn pockets of flour.
Simmer the white sauce
Bring the milk mixture to a gentle simmer, stirring regularly. It should start to thicken as the flour cooks.
Cook for several minutes until the sauce coats the back of a spoon and has no raw flour flavour. Avoid allowing milk to scorch on the base.
If the mixture becomes very thick early, add a little more milk. Cheese will make it richer and somewhat thicker, so leave some room for that change.
Reduce the heat before adding cheese
Take the pan off direct heat or turn the hob very low. Stir in the grated cheddar in several additions until each has melted.
Boiling cheese aggressively can cause its proteins to tighten and separate from fat, leaving a grainy or oily sauce.
A smooth white sauce and moderate temperature give the cheese a better chance to melt evenly. Don't rush the final stage merely because dinner is nearly ready.
Season once the cheese is melted
Taste carefully when the sauce has cooled enough for a small spoonful. Add pepper, a little mustard or a pinch of nutmeg if they suit the dish.
Mustard often deepens the flavour without making the sauce noticeably hot. Begin with a small amount rather than an entire tablespoon.
Salt only if needed. Cheese and prepared mustard may already provide enough, especially if the sauce will be mixed with salted pasta or vegetables.
Make it thicker for cauliflower cheese
For a baked vegetable dish, you may want a sauce that clings to florets instead of sliding to the bottom of the oven dish.
Start with slightly less milk or simmer the white sauce a little longer before adding the cheese. Remember that the sauce will also thicken slightly as it cools.
Don't try to repair a thin cheese sauce by stirring dry flour directly into it. That usually creates lumps.
Make it looser for pouring
If serving cheese sauce over cooked vegetables, thin it with warm milk in small amounts while stirring gently.
A pourable sauce coats broccoli or leeks without turning the plate into a solid mass. Stop thinning before it becomes watery.
The right thickness depends on the meal. There isn't one precise consistency appropriate to macaroni cheese, nachos and cauliflower cheese.
Turn it into macaroni cheese
Cook macaroni according to the packet, aiming for pasta that will remain suitable after any additional baking. Drain thoroughly.
Mix with warm cheese sauce and transfer to a dish if you want to bake it. Top with a modest amount of cheese or crumbs for a browned finish.
Avoid very dry pasta mixed with an extremely thick sauce, which can become stodgy in the oven. A slightly looser sauce is useful when the dish will continue cooking.
What if your sauce is lumpy?
If lumps appear before adding the cheese, whisk vigorously while the mixture is warm. Small flour lumps may disperse.
For stubborn lumps, push the sauce through a fine sieve before melting in the cheese. This is easier than trying to fix it once the sauce contains stringy, partly melted cheese.
Next time, add the first milk more gradually and whisk until completely smooth between additions.
What if the sauce turns grainy?
The cheese may have overheated or the chosen cheese may not melt smoothly. Take the pan off the heat and stir gently.
A little warm milk may help loosen a sauce that is beginning to tighten, but it won't always reverse separation.
Avoid boiling after cheese is added. Choose a good melting cheese and grate it finely. Low, gentle heat is the most reliable prevention.
What if the sauce becomes oily?
Some cheeses release fat when overheated. The sauce may look shiny with yellow oil collecting around the edges.
Remove it from the heat immediately and stir gently. If the emulsion has separated severely, making a fresh small white sauce and whisking the mixture into it may be worth trying.
Don't keep increasing the heat. That usually makes separation worse.
Making cheese sauce without butter
A sauce can be made with suitable oil instead of butter, using the same general roux technique. The flavour will be different but it can work.
For a dairy-free version, use a recipe developed for plant-based milk and an appropriate cheese alternative. Different products melt and thicken differently, and not every substitute works gram-for-gram.
Consider allergies and dietary requirements, especially when serving a dish that may appear vegetarian but contains cheese made using animal rennet.
Storing and reheating leftovers
Cheese sauce contains milk and is perishable. Cool promptly, refrigerate in a clean covered container and use within an appropriate short period.
Reheat gently, stirring regularly, until thoroughly hot. Add a small splash of milk if it has thickened in the fridge.
Avoid reheating over a fierce flame. The same high heat that makes fresh cheese sauce grainy can ruin leftovers.
The dependable sequence is cook butter and flour, whisk in milk gradually, simmer until smooth, then melt cheese gently off the strongest heat. Learn that and you can make an impressive range of meals from ordinary cupboard ingredients.