Combine the flour, 2 teaspoons salt, and 1 teaspoon pepper in a bowl and dredge the lamb shanks in the mixture, shaking off the excess. In a large (13-inch) Dutch oven such as Le Creuset, heat 3 tablespoons of the grapeseed oil over medium-high heat. Add 2 lamb shanks and cook for 10 minutes, turning every few minutes, until browned on all sides. Transfer the shanks to a plate, add more grapeseed oil, and brown the remaining 2 shanks.
Wipe out the Dutch oven with a paper towel, add the olive oil, and heat over medium to medium-high heat. Add the onions, carrots, celery, and rosemary and cook for 8 to 10 minutes, until the vegetables are tender. Add the garlic and cook 1 more minute. Add the tomatoes, beef broth, wine, 4 teaspoons salt, and 2 teaspoons pepper. Add the lamb shanks, arranging them so they're almost completely submerged in the liquid. Tuck in the bay leaves and bring to a simmer on top of the stove. Cover the pot and place it in the oven for 2 hours, turning the shanks once while they cook.
Stir in the orzo and return the lamb shanks to the oven for 20 to 30 minutes, until the orzo is cooked and the lamb shanks are very tender. Discard the bay leaves, stir in 2 to 3 tablespoons of white wine, and taste the orzo for seasonings. Serve hot.
This recipe has been updated and may differ from what was originally published or broadcast.