Cream Tomato Sauce

A three-minute flour-thickened tomato sauce of the plainest sort, built on a slurry rather than a roux. The whole thing hinges on how the flour goes in.

• The hinge: the slurryA quarter cup of flour stirred into a quarter cup of cream makes a thick paste rather than a loose slurry. Work it completely smooth in a bowl before it goes near the pot, and add it to the boiling tomato in a thin stream while whisking hard, or it can set into lumps you cannot break up.
• Strained tomatoThis means tomato pulp pressed through a sieve to remove skin and seeds — what a supermarket now sells as passata. Unsalted canned crushed tomatoes pushed through a strainer give the same thing.
• Cook the flour outThe recipe stops as soon as the sauce thickens, which leaves a pasty raw-flour taste. Hold it at a bare simmer for four or five minutes, stirring, until the gloss changes and the starch flavour goes.
• CurdlingCream and acidic tomato can separate if boiled hard together. The high fat of heavy cream and the flour both help hold the emulsion, but it is still safest to keep the heat moderate once the slurry goes in rather than letting it return to a rolling boil.
• ConsistencyA quarter cup of flour to two cups of liquid is the standard medium coating-sauce proportion, thick enough to nap eggs or vegetables. To take it towards a cream of tomato soup, thin with a further cup of milk or stock after thickening.
• SaltOne teaspoon in two cups is on the assertive side, and canned tomato is usually salted already. Add half, taste at the end, and adjust.
• YieldAbout two cups -- enough sauce for four servings, or two bowls of soup once thinned.