How to Make It
In a food processor, puree the chipotles and adobo until smooth. Put the chicken legs on a large rimmed baking sheet and season with salt and pepper. Coat the legs thoroughly with the puree. Cover and refrigerate overnight.
Preheat the oven to 350°. In a large skillet, heat 1 tablespoon of the oil until shimmering. Add 4 of the chicken legs to the skillet, skin side down, and brown over moderate heat, about 4 minutes per side. Transfer to a large rimmed baking sheet. Wipe out the skillet and repeat with the remaining oil and chicken legs. Wipe out the skillet again.
Melt the butter in the large skillet. Add the onion and green pepper and cook over moderately low heat until lightly browned, about 15 minutes.
Meanwhile, roast the red peppers directly over a gas burner or under a preheated broiler, turning occasionally, until charred all over. Transfer the peppers to a plate and let stand for 10 minutes. Discard the charred skin, stems and seeds and cut the red peppers into 1/2-inch dice.
Add the chicken stock to the onion and green pepper and simmer over moderate heat for 5 minutes. Add the tomatillos, tomato, garlic, cayenne and the roasted red peppers and simmer over moderate heat for 10 minutes. Season the sauce with salt and pepper and pour into 2 large baking dishes. Set the chicken legs on top of the sauce, skin side up. Bake for about 25 minutes, or until the chicken is deeply browned and cooked through. Scatter the scallions and cilantro over the chicken and serve.