Comforting Lamb Casserole

15g plain flour
0.5kg boneless shoulder or leg of lamb, trimmed of excess fat and cut into 3cm pieces
1 tbsp sunflower oil
30g unsmoked bacon lardons or pancetta
1 large onion, chopped
2 medium carrots (about 200g), peeled and cut into 2.5cm pieces
1 large celery sticks, sliced
2 garlic clove, crushed
1 tsp chopped fresh rosemary
1 tsp tomato purée
250ml chicken or lamb stock
1 bay leave

Put the flour into a large mixing bowl and season. Add the diced lamb to the bowl and toss. Heat 2 tablespoons of the oil in a flameproof casserole or large nonstick pan, add half the lamb and fry over a high heat until browned. Lift out to a plate and repeat with the rest of the lamb. Set aside.
Add the bacon to the pan and cook over a medium heat until golden brown. Add the onion stirring frequently, until golden. Add the carrots and celery, cover and cook for 5 minutes.
Uncover, add the garlic and rosemary and cook for 1 minute.
Stir a tiny bit of flour into the veg, followed by the tomato purée, stock and bay leaves, and bring to the boil, stirring. Return the lamb to the pan, part-cover, lower the heat and leave to simmer for 1¼ hours or until the lamb is tender and the sauce has thickened. Stir occasionally to make sure it’s not catching on the base. Discard the bay leaves and season to taste.