Bloom the saffron. Add the saffron to the water and set aside to bloom.
Brown the lamb shanks. Place a Dutch oven or a large pot with a lid over medium-high heat. Add 2 tablespoons of olive oil. Season the lamb shanks with salt and pepper and brown them on all sides, about 8-10 minutes. Once browned, remove the shanks from the pan and set them aside.
Cook the vegetables. Add the sliced onions to the pot and cook until golden, about 5 minutes. Add garlic, carrots, red pepper and celery and cook for a further 5 minutes, stirring regularly.
Add the spices. Stir in the turmeric and cinnamon, followed by the tomato paste. Add the bay leaves.
Braise the lamb shanks. Pour in the vegetable broth. Stir in the bloomed saffron and return the shanks to the pan. Bring the mixture to a boil, then turn down the heat to medium-low and simmer, covered, until the lamb is fall-off-the-bone tender, about 2 hours and 30 minutes. Taste and season the dish with salt and pepper before serving.
Finish and serve. Lift the shanks gently, using two forks, and place them into a serving dish. Ladle the sauce over and around the shanks and serve.
