Stir in the soy milk, then puree the soup in a blender in 2 or 3 batches until very smooth. Return it to the pan and heat over a medium flame until hot and steamy (do not let it boil), about 10 minutes
Serve with a sprinkling of fresh cilantro if desired.
Per serving: 106 calories; 2 g protein; 18 g carbohydrate; 3 g fat; 302 mg sodium; 0 mg cholesterol