Spicy Chipotle Meatballs

1.Heat the oil in a large skillet over medium heat. Add the onion and half the garlic and cook, stirring occasionally, until beginning to brown, 5 to 7 minutes. Add the tomatoes (with their juices) and chipotles; using a potato masher, beak up the tomatoes. Simmer, partially covered, until the sauce has thickened, 15 to 20 minutes. If the sauce becomes too thick, add up to 1/2 cup water.
2.In a medium bowl, combine the beef, cilantro, bread crumbs, egg, cumin, the remaining half of the garlic, 1 1/2 teaspoons salt, and 1/4 teaspoon pepper. Shape the mixture into 16 meatballs (about 2 heaping tablespoons each).
3.Heat broiler. Place the meatballs on a baking sheet and broil, turning once, until cooked through, 8 to 12 minutes. Add the meatballs to the sauce. Serve with a sprinkle of additional cilantro.