Moroccan Lamb Shanks with Pomegranate

Name: Moroccan Lamb Shanks with Pomegranate
Ingredients: 1 teaspoon coriander seeds; ½ teaspoon cumin seeds; ½ teaspoon fennel seeds; ¼ teaspoon red pepper flakes; Pinch of saffron (optional); Kosher salt, freshly ground black pepper; 2 lamb shanks (about 2½ pounds); 1 tablespoon cornstarch; 1 tablespoon olive oil; 1 medium red onion, cut into 1-inch wedges; 2 medium carrots, cut into 2-inch pieces; 1 large leek, white and light-green parts only, cut into 2-inch pieces; 1 cinnamon stick; 8 sprigs thyme; 1½ cups pomegranate juice; 1½ cups homemade chicken stock, low-sodium canned, or water; ¼ cup pomegranate seeds; ¼ cup mint leaves; Flaky sea salt; A spice mill or a mortar and pestle