Use this recipe as a dressing for Potato and Heirloom Tomato Salad.
Heat broiler. Position rack about 6 inches from heat. Place poblano and tomatillos on a small baking sheet with sides. Place under broiler until tomatillos soften, and pepper skin blackens, tossing frequently for about 5 minutes. Remove from oven, place pepper in a small bowl, and cover with plastic wrap to steam, about 10 minutes.
When cool, remove husks from tomatillos, and place in bowl of food processor. Remove seeds from pepper and scrape off skin. Add half of pepper to processor with tomatillos, along with cilantro, olive oil, lime juice, salt, pepper, and sugar. Puree until smooth and emulsified, about 30 seconds. Set aside. Cut remaining half pepper into 1/2-inch pieces, and set aside for salad, if using.