Roast the peppers by placing them on an open gas flame, turning them frequently with tongs until all sides are charred black, about 7 to 10 minutes. (Alternately, the peppers can be roasted under a broiler, or on top of a gas or charcoal grill.) Place the blackened peppers in a plastic or paper bag, and let rest until cool enough to handle, about 15 minutes. Peel the peppers, remove the seeds and stems and roughly chop.
Combine the peppers, shallots, cilantro, basil, garlic, crushed red pepper, vinegar, salt, and pepper in the bowl of food processor or blender, and process for 20 seconds. With the machine running, add the oil through the feed tube in a steady stream and process until thick and smooth. Drizzle into the Asparagus Soup, and transfer any remaining into an airtight container and store in the refrigerator for up to 1 week.
Yield: about 3/4 cup