Preheat your oven to 150˚C/Gas 2. Rub the brisket with a little oil and season all over with a little salt and pepper. Heat a flameproof casserole, one with a lid, that one fits the meat fairly snugly. Fry the brisket to seal and brown it on all sides (this will take a good few minutes, longer than you might think).
Transfer the brisket to a plate. Add the carrots, onions, celery to the same pan. Fry on a low heat, stirring now and then, for 10 minutes to get them on their way.
Add the flour and stir for 2 minutes. Add the bottle of ale and thyme. Pop the brisket back in, with any juices from the plate. You want the liquid to be about two-thirds up the brisket, so top up with a little water or stock if needs be.
Season with salt and pepper, bring up to a low boil, pop on a lid and cook in the oven for 4 hours until tender. Remove the beef and slice half of it to serve 4, saving the rest for leftovers.
This is a basic recipe but by all means add extras if you like; a little garlic, some bay, use stock instead of ale if you prefer, or a mix of red wine and stock, it’s up to you.