Preheat the broiler. Put poblano on a baking sheet and broil as close to heat source as possible, turning once, until charred all over, about 6 minutes. Transfer poblano to a small bowl, cover tightly with plastic wrap and let stand for 5 minutes. Rub skin off of the chile with a paper towel and discard the stem and seeds. Cut the poblano into 1/4-inch dice. Transfer all but 1 tablespoon to a medium bowl. In a metal baking pan, broil the tomatillos, turning once, until lightly browned, about 4 minutes. Transfer the tomatillos to a food processor and puree.
Add the tomatillo puree to the diced poblano along with the onion, garlic, chopped cilantro, lime juice and half of the avocado; mash well with a fork. Add the remaining avocado and mash lightly. Season with salt and pepper. Serve topped with the reserved 1 TBS of diced poblano and the cilantro leaves.
From the August 2006 issue of Food & Wine.