Quick answer: Lumps form when flour hits hot liquid all at once. Either cook the flour into the fat first to make a roux, then add stock gradually while whisking, or mix cornflour with cold water into a smooth slurry before stirring it in. Keep whisking as it thickens, and strain if any lumps remain.
Lumpy gravy is nearly always a mixing problem, not a cooking one. Lumps form when dry flour meets hot liquid and the outside turns to paste before the inside can disperse. Avoid that one moment and smooth gravy is guaranteed.
Method 1: the roux (best for roast dinners)
This uses the flavour-packed fat and juices left in the roasting tin.
- Spoon off most of the fat, leaving about 2 tablespoons and all the browned bits in the tin.
- Sprinkle in 2 tablespoons of plain flour and stir over a low heat for a minute or two to cook out the raw taste — you want a smooth paste.
- Add hot stock a splash at a time, stirring or whisking constantly. Let each addition become smooth before adding more. Adding it gradually is the whole secret.
- Simmer for a few minutes until glossy, then season.
Method 2: the cornflour slurry (quick and reliable)
Ideal when you just want gravy fast, or need it gluten-free.
- Mix 1 tablespoon of cornflour with 2 tablespoons of cold water into a smooth, lump-free paste.
- Bring your stock or pan juices to a simmer.
- Stir the slurry in gradually, whisking, and cook for a minute or two until thickened. Add a little more slurry if you want it thicker.
Always slake cornflour with cold water first — tipped in dry, it clumps instantly.
Keep whisking
Whichever method you use, a balloon whisk beats a spoon. Whisk steadily as the gravy comes up to a simmer and thickens; constant movement stops any flour settling and catching.
Rescue lumpy gravy
If lumps appear anyway, don’t start again:
- Whisk hard — many small lumps break up with vigorous whisking.
- Pass it through a sieve into a clean pan.
- Blitz with a stick blender for a completely smooth finish.
Finishing touches
Taste and adjust: a splash of the vegetable cooking water, a dash of soy or Worcestershire sauce for depth, and salt and pepper to season. Simmer to your preferred thickness and serve hot.