Place the corn on a grill grate to char or place in a dry cast iron skillet over medium-high heat. Turn occasionally to evenly char, around 4 minutes. Remove and transfer to a cutting board. When cooled, cut the corn from the cob. Set the kernels aside.
Place the cob, stock, half of the onions, garlic and salt in a large saucepan over medium-high heat. Bring to a boil and reduce to 3 cups. Remove from the heat, discard the corn cob, stir in the jalapeno and allow to cool for 20 minutes.
Pour through a fine meshed sieve into a large bowl, pressing the solids with a wooden spoon to extract moisture. Discard the solids and return the stock to the saucepan.
Stir in the remaining onions, onion salt or garlic salt, white pepper, one of the avocados, lime juice and 1 teaspoon of the lime zest. Puree with an immersion blender until smooth. Stir in the remaining avocado that has been chopped along with the reserved corn kernels. Transfer to a serving bowl, cover and refrigerate at least 1 hour.
When ready to serve, ladle the soup into chilled bowls. Whisk together the Mexican crema and olive oil until smooth. Drizzle on top of each serving. Garnish with a sprinkle of cilantro and any remaining lime zest.
Recipe by The Tennessee Magazine at https://www.tnmagazine.org/go-for-the-green-with-avocados/