Pre heat oven to 150C.
Remove as much fat as possible from the veal.
Dust veal in flour, and reserve left over flour.
Heat oil in a large flameproof casserole dish, and fry veal in batches until brown and remove to a plate.
Add leek and carrots to dish and fry over medium heat for 1-2 mins. Add reserved flour and fry for 1 min.
Add mushrooms and fry for 2-3 mins.
Add tomato paste, garlic and thyme and fry for a further 1-2 mins.
Add wine and simmer for 3-4 mins or until reduced slightly - making sure to scrape any brownings from the base of the dish as you go.
Add stock and bring to boil. Add back the veal and any juices.
Make a cartouche (a fancy name for a circle of baking paper! - see my notes) from baking/grease proof paper to sit on top of veal - this keeps all of the meat just submerged and moist for the whole cooking time.
Bake with lid on for 2 hours.
Remove veal from sauce and remove any fat and bones. Roughly shred/chop meat.
Meanwhile simmer sauce on stove top for 5 mins to thicken.
Add back meat and serve with mashed potato or pasta.