How to Make It
In a food processor, combine the avocados, stock, 1 cup of water and 1/4 cup of the lime juice and puree until very smooth. With the machine on, gradually add the heavy cream. Strain through a fine sieve into a large bowl, then season with salt. Cover and refrigerate until well chilled, about 1 hour.
Meanwhile, in a medium saucepan, heat ¼ inch of canola oil until shimmering. Add the serranos and fry over moderately high heat, stirring, until lightly browned and crisp, 1 to 2 minutes. Using a slotted spoon, transfer to paper towels to drain.
In a medium bowl, gently toss the crab with the remaining 1 tablespoon of lime juice. Ladle the chilled soup into bowls and top with the crab and crispy serranos. Garnish with crema and cilantro and serve.