Soup: Heat a heavy saute pan over medium-high heat. Add the tomatoes, peeled onion, and unpeeled garlic cloves. Roast, turning frequently, until the garlic is soft, about 10 minutes. Remove the garlic when soft, but slightly blackened. Peel the garlic and set aside. Add the chile and continue to cook for another 2 to 4 minutes. Remove the onion and set aside. Continue to cook the tomatoes until charred and blackened, another 5 minutes. Put the garlic, chile, onion, tomatoes, tortillas, and 2 cups chicken broth in a blender. Blend until smooth. Pour into a large saucepan and add the remaining 4 cups chicken broth. Bring the mixture to a boil, reduce the heat and simmer for 20 minutes. Season with salt and pepper, to taste.
Tortilla strips: In a medium, heavy skillet, pour enough oil to reach a depth of 1/2 an inch. Heat over medium-high heat until very hot, but not smoking. Add the tortilla strips in batches and fry until golden and crisp, about 2 minutes. Remove with a slotted spoon and drain on paper towels. Set aside.
To serve, ladle the soup into 6 individual serving bowls. Serve whole chipotle chiles, Mexican sour cream, avocados, cheese, and tortilla strips on the side.
BLENDING HOT LIQUIDS: 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; that 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. The blended corn tortillas act as thickeners. This soup should not be as thick as a cream soup, but should have some body.
This recipe has been updated and may differ from what was originally published or broadcast.