First melt the dripping in a thick cooking pot and, when it's hot, put in the meat and sear and brown it all over, then transfer it to a plate.
Next lightly brown the onions, carrots, celery and swede, then remove them temporarily to the plate, too. Next, empty all the fat from the pot, then replace the brisket and arrange the vegetables and mushrooms around the meat. Add the hot stock, bay leaf and thyme and a little salt and pepper. Cover with foil and a tightly fitting lid and as soon as you hear simmering, place in the centre of the oven and leave for about 3 hours.
When ready, place the meat and vegetables on a warmed serving dish, then bring the liquid to the boil and boil briskly until reduced slightly. Mix the butter and flour to a paste, then add this to the liquid and whisk until the sauce thickens. Serve with the meat and some sharp English mustard.
Pre-heat the oven to gas mark 1, 275°F (140°C).
Using a fan-assisted oven? Click here