Lamb Tagine with Tomatoes and Caramelized Sweet Onions

INGREDIENTS

• 1 teaspoon ground cinnamon
• 9 cups chopped sweet onions (such as Vidalia or Maui; about 3 pounds), divided
• 4 tablespoons chopped fresh Italian parsley, divided
• 1/4 cup olive oil
• 1 teaspoon ground ginger
• 2 cinnamon sticks
• 2 cups water
• 1 teaspoon salt
• 1 teaspoon coarsely ground black pepper
• 3 pounds boneless lamb stew meat, cut into 3/4- to 1-inch pieces
• 1/8 teaspoon crumbled saffron threads
• 4 cups chopped plum tomatoes (about 1 1/2 pounds)