Chicken Tinga Tacos

In a large enameled cast-iron casserole, heat the oil. Add the onion, garlic, cumin and coriander. Cook over moderately high heat until the onion is softened. Add the stock, tomato puree, oregano and bay leaves; bring to a boil. Add the chicken, cover partially and simmer until cooked, 35 to 40 minutes. Meanwhile, preheat the oven to 400 °. In batches, fold the tortillas in half and stuff them between the cups of an inverted muffin tin to form shells. Bake for 15 minutes, until crisp. Remove the chicken from the sauce and shred the meat. Return the meat to the sauce and simmer for 10 minutes. Discard the bay leaves and oregano sprig. Stir in the vinegar and season with salt and pepper. Serve in the taco shells with cilantro, lime and onion.