In a 6-qt. electric or stove-top pressure cooker combine the first 11 ingredients (through cayenne pepper). Lock lid in place. Set an electric cooker on high pressure to cook 6 minutes. For a stove-top cooker, bring up to pressure over medium-high heat; reduce heat enough to maintain steady (but not excessive) pressure. Cook 6 minutes. Remove from heat. For both models, let stand 15 minutes to release pressure naturally. Release any remaining pressure. Open lid carefully. Using a handheld immersion blender, blend soup until smooth. (Or let soup cool slightly. Transfer soup in batches to a food processor or blender. Cover and process or blend until smooth.) Stir in coconut milk. Top servings with cilantro if desired.