Slice the avocados through the center and around the pit. Twist the halves and pull them apart. Knock the heel of the knife into the pits and twist them out of the avocados. Discard the pits. Scoop the flesh out of the peels with a spoon and place that in the bowl of a food processor. Discard the peels. Here is a short video that shows just how to cut and deseed an avocado.
Add the sour cream, cilantro leaves, lime juice, garlic powder, salt, and cayenne (if using) to the food processor.
Process until smooth and creamy.
Store in an airtight container in the refrigerator until ready to serve. Use the sauce as soon as possible.