Cast Iron Roasted Leg of Lamb with Rhubarb Sauce

Name: Cast Iron Roasted Leg of Lamb with Rhubarb Sauce
Ingredients: 6 green cardamom pods; 5 allspice berries; ½ cinnamon stick , broken in half; 1½ teaspoons coriander seeds; 1 teaspoon cumin seeds; 1 teaspoon fennel seeds; 1 teaspoon black peppercorns; 1 teaspoon ground ginger; 2 tablespoons kosher salt; 1 (4½- to 5-pound) boneless, butterflied leg of lamb; 2 tablespoons vegetable oil; 1½ cups water; 2 shallots , chopped; 1 pound rhubarb , cut into ¾-inch pieces; ¾ cup dry red wine; ½ cup sugar; ½ cup golden raisins; ¼ cup torn fresh mint