In a blender combine Achiote paste, garlic, cumin, cinnamon, orange juice, lime juice, vinegar, salt and pepper. Puree until smooth. Pour into a nonreactive baking pan, add the chicken and turn to coat. Cover and marinate in the refrigerator for at least 2 hours and up to 24 hours. Preheat oven to 375 degrees. In a heated, dry, cast iron skillet char onion slices until blackened on both sides. Remove and char tomato slices until blackened on both sides. Reserve. Cut six 16 x 14-inch sheets of heavy-duty aluminum foil. Take banana leaves, and cut into 10-inch squares. Toast squares over a burner to soften, about 2 seconds on each side . Place banana leaves on top of each piece of foil. Remove chicken from marinade, reserving marinade, and place a piece on each foil piece or banana leaf. Top each with two tomato slices and one onion slice. Wrap and seal banana leaf and the foil to enclose. Place on a baking sheet and bake for 45 minutes. Meanwhile, in saucepan melt butter. Saute the diced onions until golden brown. Stir in the reserved marinade and bring to a boil. Cook, stirring frequently, for about 5 minutes. Add chicken stock and cook for 10 minutes longer. Reserve. When the chicken in ready, remove from oven and open the packets. Transfer the chicken, with the banana leaves if using, to serving plates. Pour any excess juice from the pan into the sauce. Pour sauce over chicken and serve.

* Achiote paste is a bright orange seasoning paste from the Yucatan made of ground annatto seeds, oregano, cumin, cinnamon, pepper and cloves. It is often thinned with vinegar or citrus juices for marinades and sauce and should always be cooked first to remove any chalkiness.