Braised lamb shanks with tomato and fennel

4 1 1/ 2 -pound lamb shanks, trimmed
Coarse salt and freshly ground pepper
1/ 2 cup all-purpose flour
4 tablespoons extra-virgin olive oil
2 tablespoons unsalted butter
2 medium onions, sliced 1/ 4 inch thick
1 large leek, white and light-green parts only, washed well, sliced into 1/ 4 -inch half-moons
4 garlic cloves, thinly sliced
1 cup dry red wine
2 cups homemade or low-sodium storebought chicken stock
1 28-ounce can peeled whole plum tomatoes, drained
2 tablespoons tomato paste
1 tablespoon fresh thyme leaves
2 dried bay leaves
2 medium fennel bulbs, sliced 1/ 4 inch thick

Preheat the oven to 375ï€ F. Season the lamb all over with salt and pepper. Place the flour in a shallow bowl. Dredge the lamb in the flour, turning to coat evenly; shake off excess. Heat the oil and butter in an 8-quart Dutch oven or skillet over medium heat. Working in two batches, cook until the shanks are well browned, about 5 minutes per side. Transfer the shanks to a large plate; drain off all but 2 tablespoons fat from the skillet.
Place the skillet over medium heat; add the onions and leek, and saute until they are lightly browned, about 6 minutes. Add the garlic; cook 4 minutes more. Add the red wine; deglaze the pan by scraping up any browned bits with a wooden spoon. Return the shanks to the skillet, and add the chicken stock, tomatoes, tomato paste, thyme, and bay leaves. Bring to a boil; cover, and place in oven. Braise 2 hours; add the fennel, and cook 30 minutes.
Using a slotted spatula, transfer the shanks and vegetables to a large bowl. Cover; set aside. Using a ladle, skim the fat from the surface of the cooking liquid; cook over medium heat until the liquid is thickened, 5 to 7 minutes. Return the shanks and vegetables to the pan; cook until heated through. Remove from heat, and season with salt and pepper.
SERVES 4