Lightly oil a rimmed baking sheet or baking pan and roast tomatillos and jalapeno or chilies under a hot broiler, 4 inches or so from the heat source, 3 to 4 minutes, or until they are blistered and splotchy brown with, maybe, a few black spots. Turn them and roast on the other side. Cool, then transfer tomatillos and chilies to a food processor fitted with the metal blade or blender along with any of the juices on the pan. Process or puree until smooth.
Meanwhile, over medium heat in a heavy-bottomed saucepan, heat 2 tablespoons olive oil. Add onions and garlic and cook, stirring, about 6 minutes until golden brown. Raise heat to medium high, add tomatillo puree and cook 3 minutes until sauce darkens and is very thick. Add broth, brown sugar and 1/4 cup cilantro. Stir, reduce heat and simmer, uncovered, 10 minutes or until sauce thickens. Season with salt and pepper. Set sauce aside.
Season chicken liberally with salt and pepper. Heat 3 tablespoons olive oil over medium-high heat in an oven-proof skillet large enough to hold chicken in one layer. Add chicken, skin side down, and cook 5 minutes until skin is richly browned. Turn and cook on bone side 2 minutes or so. Remove chicken from pan and pour out all but 1 tablespoon fat. Add tomatillo sauce and bring to a simmer. Nestle chicken pieces, skin side up, in the sauce, place in preheated 375-degree oven and bake 15 minutes, or until chicken is cooked. (Check with point of a small knife near the bone to make sure chicken is cooked through.)
Place one piece of chicken in each of four shallow bowls, spoon sauce around, top with crema or queso fresco and sprinkle remaining cilantro over.