Roast the chiles and tomatillos under the broiler until blackened on both sides, about 10-12 minutes, turning once. Once blackened, place the chiles in a paper sack or plastic food-storage bag, close it tight and let the chiles steam for 20 minutes. Place the tomatillos in a blender.
After the chiles have steamed, remove from the bag and rub off the skin. Remove the stems and seeds from both the chiles and add to the blender.
Add the avocado, garlic, cilantro, lime juice, and water to the blender. Puree until smooth, then add salt to taste (I usually start with 1/2 teaspoon kosher salt). If too thick, feel free to thin it with more water.
Will keep in the refrigerator for 3 days.
Green chile creamy avocado salsa | www.homesicktexan.com