As a kid who only ever ate tortilla soup in various gringo-fied Mexican-ish restaurants on the Upper West Side and perhaps the occasional New Jersey strip mall, I figured the dish was about as authentically Mexican as ranchero burgers and fried ice cream (A.K.A. not at all). I was right and wrong.
Certainly, the jarred-salsa-watered-down-with-chicken-broth versions I ate garnished with fried tortilla strips, avocado, and not a hint of chili were in the Mexican't camp. But there are more authentic, more complex, more compelling versions of the dish.
According to a 2005 Los Angeles Times article, the exact origins of the dish have not actually been pinpointed, but it stemmed from somewhere in the Mexico City area, making its way to North to California and Texas by the mid 20th Century. By the 70's and 80's, it was a staple on Mexican and Tex-Mex menus all over the southern United States.
The most basic version starts as good chicken broth enriched with a puree of roasted tomatoes and onions, garnished with picked chicken meat and crunchy fried tortillas. For my version, I start by doctoring up some storebought broth with a few aromatics and chicken bones (you can, of course, start with homemade broth and it'll be all the better). A 30-minute simmer is enough to lend the broth some extra body and flavor and to just-cook the chicken breast meat so that it remains tender and moist when you shred it.
Fresh corn is not always an ingredient in the soup, but I find it impossible to resist this time of year. I add the corn cobs to the simmering stock for flavor (read more on that technique here).
Rather than the canned tomatoes that many recipes call for, broiling a few whole ripe tomatoes while the stock simmers gets you a much deeper, richer, smokier flavor as bits of charred tomato skin make their way into the soup. Similarly, using chili powder might be alright in a pinch, but for maximum fruity-rich chili depth, I use whole dried ancho chilis simmered in the broth.
Once the tomato-chili-broth mixture is cooked, it's a simple matter of sauteeing a few more aromatics—onion, garlic, poblano pepper, the corn kernels, and a pinch of cumin and oregano—adding the broth back, picking the chicken meat, and serving, along with a handful of fresh cilantro (or epazote, if you can find it), scallions, diced avocado, and fried tortilla strips (yes, you can use good chips). For an extra-hearty soup, a can of black beans does nicely.