How do I thicken gravy at the last minute without lumps?

Thin gravy is nearly always discovered at the worst possible moment. All three of the real options work in under five minutes, and the choice between them is about what the gravy has to do next — be served immediately, sit in a warm jug for twenty minutes, or be reheated tomorrow.

What you'll need

• Cornflour (optional)
• Plain flour and soft butter (optional)
• Whisk
• Sieve (optional)

Step by step

1. Get the gravy to a proper simmer first.No thickener works below about 60°C, and a slurry stirred into barely warm gravy simply sits there and then seizes into lumps when it finally heats. Bring it to a gentle simmer before you add anything.
2. For speed, use a cornflour slurry.Two teaspoons of cornflour whisked completely smooth into two tablespoons of cold water, then poured into the simmering gravy in a thin stream while whisking. It thickens within a minute. Never tip dry cornflour into hot liquid.
3. For flavour, use a beurre manié.Knead equal weights of soft butter and plain flour into a paste — 15g of each thickens about 500ml. Drop it in a pinch at a time, whisking, and simmer for two minutes after the last piece. The fat keeps the flour particles separate so it cannot lump, and the butter enriches the gravy.
4. For depth, just reduce it.Boil it hard in a wide pan. Five minutes takes a noticeable amount of water out and concentrates the flavour rather than diluting it. The catch is that it concentrates the salt too, so taste before you decide.
5. Give it two minutes at a simmer after adding anything.Cornflour reaches full thickness almost immediately but tastes raw and chalky if it is not cooked for a minute. Flour needs two. Neither is a long wait and both change the taste.
6. Judge it in the jug, not the pan.Gravy thickens as it cools and it is always thicker in a warmed jug on the table than it looked at the boil. Stop slightly thinner than you want.
7. Sieve it if anything has gone wrong.A pass through a fine sieve removes lumps in seconds and nobody at the table will know. A stick blender does the same job and also emulsifies any loose fat back in.

Tips

• Mashed potato or a spoonful of the roast's vegetables blitzed into the gravy thickens it and adds flavour, and is invisible in a dark gravy.
• If the gravy is thin because there was too much liquid in the tin, pour some off before thickening rather than thickening all of it. You want less gravy that tastes right, not a lot that tastes of nothing.
• Cold water for the slurry, always. Warm water starts gelatinising the starch in the cup and it goes lumpy before it reaches the pan.
• Keep a small block of beurre manié in the freezer through the winter. It thaws in a minute and turns any thin sauce around.

Alternatives

• Cornflour slurry: Fastest and glossiest, and it keeps the gravy translucent. Weakness: it thins if held simmering for a long time and thins again on reheating, so it is the wrong choice for gravy you intend to keep.
• Beurre manié: Equal weights of soft butter and flour kneaded together. Cannot lump, adds richness and gloss, and survives holding and reheating. Needs two minutes of simmering to lose the raw flour note.
• Reduction: Adds no thickener at all, and concentrates flavour rather than diluting it. Slowest, and it concentrates salt, so it is only right when the gravy is under-seasoned to begin with.
• A spoonful of instant gravy granules: Perfectly effective as a thickener in an emergency, since granules are largely starch. Whisk them into a little cold water first. They bring salt and colour with them, so taste before adding more.

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