A bowl of Mexican soup

Classic tortilla soup, the way you'd find it in Mexico City, is simply good chicken broth combined with roasted tomatoes, onion, garlic, chiles and tortillas, cut into strips and fried. It's wonderfully satisfying, "a sort of soul food soup," as Mexican cooking authority Diana Kennedy puts it.

In California, it's often made with a tomato base thickened with ground tortillas, but there are variations, such as a bean soup enriched with crunchy strips of fried tortillas.

"To be really authentic, the soup should have only a little white onion, raw not cooked, blended with roasted tomato," says Kennedy, speaking from her home near Zitacuaro in the state of Michoacan.

The blend is fried, "to intensify the flavor," she says. "Then it goes into the broth." In addition to chile and tortillas, the soup ought to include epazote. "A tortilla soup without epazote is not worth eating, to my mind. But I'm a purist," she says.

Oddly, no one knows where tortilla soup came from, not even Kennedy. "It's certainly not all over Mexico," she says. "It's in the center, around Mexico City, the home of tortilla soup."

Although Dan Strehl, culinary historian and translator of "Encarnacion's Kitchen" (the 2003 cookbook drawn from Encarnacion Pinedo's 1898 California cookbook "El Cocinero Espanol") can't pinpoint the arrival of tortilla soup in California, it had certainly made its way north by the mid 20th century. It appears in "Elena's Famous Mexican and Spanish Recipes," published in San Francisco in 1944. That recipe, by Elena Zelayeta, doyenne of Mexican cooking in California, is a simple combination of broth, tomato puree and tortilla strips, to which she added mint leaves.

In Southern California, tortilla soup has been on the menu at 80-year-old Ojai Valley Inn longer than anyone on the staff can remember; it started to appear in haute versions in other restaurants in the 1980s, when regional Southwestern flavors were championed by chefs such as John Sedlar.

Today, compelling tortilla soups can be found at several Los Angeles Mexican restaurants. Jaime Martin del Campo and Ramiro Arvizu of La Casita Mexicana in Bell riff on a classic central Mexican version by pureeing guajillo chiles along with tomatoes. They grind fried tortillas with the mixture too, which amplifies the corn flavor.