Strain the cooking liquor through a sieve to separate the onions from the liquid.

Put the onions in jug, add a little of the reserved liquid and whizz together with a stick blender. Add more liquid as necessary to make a gravy of your desired consistency.

Transfer to a saucepan and gently reheat. Check seasoning and add salt and pepper to taste.

Put the cooked, sliced brisket on microwaveable plate and heat for approx 1 minute.

Serve the warmed brisket with the onion gravy poured over.