Juice from 1 lime. See "How To Juice Limes" for an easy quick way to Juice limes.
Place sour cream, mayonnaise, chopped cilantro, lime juice and zest in a food processor and process for 30 seconds until smooth. Cayenne Pepper is optional. Add if you like a little bit of spice.
Use as a dip for Chicken Fajitas, Taco's, Enchiladas and more. Store in refrigerator.