Using a large knife, carefully scrape the kernels off the corn cobs and set aside, reserving the cobs.
Using a food processor fitted with the steel blade, or a large knife, coarsely chop the garlic, onion, jalapeno pepper and corn kernels. Reserve.
In a large soup pot, heat the oil over medium-high heat and sear the chicken until just browned on both sides. Add the tortilla squares, and cook over low heat until they are slightly crisp. Stir in the chopped vegetable mixture and pasilla pepper and simmer just until the vegetables are coated with the oil. Do not brown.
Add the tomatoes, tomato paste and 2 teaspoons of the cumin and continue to simmer for about 10 minutes to maximize the flavor. Slowly pour in the stock and cook over low heat until the soup is reduced by 1/3 and the chicken breast is cooked through.
Remove the chicken breast and set aside. When cool enough to handle, slice chicken into very thin strips. Meanwhile, puree the soup, in batches, in a blender* or food processor until smooth. At this point, the soup can be passed through the fine strainer if desired.
Ladle the soup into soup bowls and garnish with tortillas, avocados, chicken, cheese, and cilantro.
*When blending hot liquids: Remove liquid from the heat and allow to cool for at least 5 minutes. Transfer liquid to a blender or food processor and fill it no more than halfway. If using a blender, release one corner of the lid. This prevents the vacuum effect that creates heat explosions. Place a towel over the top of the machine, pulse a few times then process on high speed until smooth.