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CHEESE sauce is one of the first things I remember learning to cook as a child. You melt butter in a pan, whisk in the flour and cook for 2 minutes. Then, gradually add the milk, whisking vigorously to avoid lumps. Simmer until it thickens, then mix in the cheese.

I must have made macaroni cheese this way dozens of times, but I might never do so again since learning of an ingenious shortcut.

Before I get to that, let’s consider why we need flour in a cheese sauce in the first place. The starch in flour plays two important roles here. One is to thicken the sauce. When heated up in milk or water, starch granules swell and burst, releasing amylose and amylopectin molecules throughout the liquid. These long chains of carbohydrate get tangled together, forming a loose matrix that raises the liquid’s viscosity.

Starch’s other role is to stabilise the melted cheese. Cheese contains water and milk fat, which has a tendency to separate out when it melts, forming a greasy layer on the surface. When cheese is heated up, the molecules of the protein casein it contains can link together with calcium to form long chains, making the cheese stringy.

contain salts such as sodium citrate that stabilise the emulsion, helping to ensure they melt smoothly rather than splitting. The negative ions in the salt associate with calcium ions in the cheese, preventing the latter from forming links between protein molecules and thus preventing stringiness. Starch performs a similar role, albeit less effectively. The starch matrix helps the fat globules remain dispersed, so the fat doesn’t separate, and ensures the protein molecules can’t easily link together.

You can and use it to make a smooth cheese sauce without flour. But you can also ditch the flour by relying on another source of starch: pasta.

Pasta releases lots of starch into the water as it cooks. Chefs often add a splash of this starchy water to oil-based sauces to help them emulsify and become creamy. – pasta with cheese sauce the Italian way – isn’t made with a flour roux, but by mixing grated pecorino romano with starchy pasta water, along with some olive oil or butter.

That brings us to the clever shortcut to macaroni cheese: instead of making a flour roux, cook the pasta in milk, then stir the cheese into the same pot. The starch released from the pasta will emulsify and thicken the sauce without having to add any flour. This makes for a sauce that tastes more cheesy and less floury. I learned this from Noor Murad and Yotam Ottolenghi’s Shelf Love.

Here is a basic recipe using the same technique. Put the pasta, milk, water, butter and salt in a large saucepan. Bring to a simmer, then turn the heat low and cook for 8 to 10 minutes. Stir in the cream and cheese, check the seasoning and serve.

Sam Wong is assistant news editor and self-appointed chief gourmand at New Scientist. Follow him @samwong1