In a bowl, mix the BBQ sauce with all the other ingredients up to and including the beef stock. Add the rosemary. Press in the garlic.
Cut the beef brisket in half crosswise, season Heat the oil in a cooking pot, brown the meat all over for approx. 10 mins. on a medium heat, only turning when a crust has formed.
Chop the carrots, quarter the leek and cut lengthwise into strips approx. 8 cm long. Roughly chop the onion. Add the vegetables to the meat.
Pour the stock into the pot. The meat should be approx. three-quarters covered.
Cover and braise for approx. 3 hrs. in the lower half of an oven preheated to 180°C.
Remove the meat and vegetables, cover and set aside.
Reduce the cooking stock to approx. half the amount, serve the meat and vegetables with the stock.