Step #1 Broil peppers on an aluminum foil wrap-lined baking sheet 5 inches from heat about 5 mins on each side or until peppers look blistered.
Step #2 Place broiled peppers in a heavy-duty zip-top plastic bag; seal bag & let peppers stand about 10 mins to loosen skins.
Step #3 Peel peppers; remove & discard seeds.
Step #4 Process peppers, & next 5 ingredients in a food processor/blender or mixer until mixture is smooth, cooked tomatillos, 1 c chicken broth, stopping to scrape down sides.
Step #5 Transfer mixture to a saucepan, & cook over med-heat/flame 5 mins.
Step #6 Slowly stir in the remaining 1/2 c chicken broth, & cook about 10 mins or until sauce is thickened.