Beef & veg casserole

Ingredients (5 servings): 2 celery sticks, thickly sliced 1 onion, chopped 2 really big carrots, halved lengthways then very chunkily sliced 5 bay leaves 3 sprigs thyme 1 tbsp vegetable oil 1 tbsp butter 2 tbsp plain flour 2 tbsp tomato purée 2 tbsp Worcestershire sauce 2 beef stock cubes, crumbled 850g stewing beef (brisket…