Microwave the tomatillos on 70 percent power for four minutes. Let them cool, then peel them and cut into quarters. Remove the seeds, then chop.
Combine the tomatillos in a non-metallic bowl with all the other ingredients except the avocados. Then scoop the meat out of the avocados and add it to the mix. Stir.
In batches, process the mix in a food processor to a rough puree.
Whisk in the chicken stock (or water). Taste and adjust salt and pepper levels. (Use hot sauce for the pepper part.)
Place a piece of plastic wrap over the surface of the soup, and refrigerate for no more than an hour. Serve in chilled bowls. Garnish with sour cream, chopped cilantro, chopped fresh tomato, and chopped onion.