In a blender or food processor, puree the cilantro, oil, and salt. Pour the mixture into a fine-mesh sieve set over a bowl and let it drain for 15 minutes. Store the oil in an airtight container at room temperature for up to 5 days. I used a a plastic squirt bottle to store the oil in. It works great for adding swirls into the soup.
CHILLED AVOCADO SOUP
Heat a dry skillet over medium-high heat and roast the whole corn, turning occasionally, until charred in spots. Transfer the corn to a cutting board and cut the kernels from the cob. Cut the cob into thirds.
Bring the kernels, cob pieces, broth, garlic, onion and 1½ teaspoons salt to a boil in a large saucepan and boil until the liquid is reduced to about 3 cups, about 20 minutes. Remove from the heat and cool, uncovered. Discard the cob pieces.
In a blender, puree the corn mixture. Add 1 of the avocados and 2 tablespoons of the lime juice to the blender; puree until smooth. Season to taste with salt. Transfer to a covered container and chill the soup for at least 1 hour, until very cold.
To serve, dice the remaining avocado into small cubes and gently mix with the remaining tablespoon of lime juice. Ladle the soup into bowls, dividing the avocado among the bowls, then drizzle each with a little sour cream (thinned with water) and a swirl of cilantro oil. Use plastic squirt bottles for the sour cream and cilantro oil. Makes it a lot easier to add swirls into the soup. Use a butter knife to spread out the swirls into a decorative pattern.