Bring 2 quarts of water to boil in a large pot. Add the tomatillos and simmer until soft, about 10-15 minutes. Drain, and remove their papery husks. (The book says to husk them before boiling but I think they come off easier after boiling.)

Cut tomatillos in half, and place them along with the remaining ingredients in a blender/food processor. Blend on high until just smooth. Use at room temperature, or cover and refrigerate. It will keep, refrigerated, for up to 1 week.