In a medium size bowl, mash together the achiote paste, garlic, orange juice, lime juice, bay leaves, cumin, cinnamon, thyme, oregano, salt, and pepper with a fork. Add the pork, toss to evenly coat and marinate, at room temperature, at least 4 hours.
Preheat the oven to 300 degrees. Heat a dry cast iron skillet over high heat. Char the onion until blackened on both sides. Char the tomatoes on both sides. Reserve.
Line a large baking dish with one layer of the banana leaves or foil. Arrange the pork in an even layer and top with the onions, tomatoes and chiles and all the marinade. Cover with more banana leaves and wrap the dish tightly in foil. Bake for 2-1/2 hours or until the pork is tender and moist. Remove from oven and let sit 10 minutes. Unwrap and serve with pickled shallots.
c.1996, M.S. Milliken & S. Feniger, all rights reserved