Over an open flame gas burner or under a preheated broiler, roast the poblanos, turning them occasionally, until the skins are lightly but evenly charred. Steam the poblanos until cool in a closed paper bag. Rub away the burned skins, slit the poblanos open along one side and discard the seeds. Open each poblano out flat.
In a small, heavy skillet over low heat, toast the oregano, stirring often, until it is fragrant and lightly browned, about 5 minutes. Remove and cool.
In a medium skillet over moderate heat, warm 3 tablespoons oil. Add the onions, garlic, cumin and cooled oregano. Cover and cook, stirring once or twice, until almost tender, about 10 minutes. Add the stock, salsa verde, chiles and 2 teaspoons salt. Bring to a simmer, then lower the heat, partially cover, and cook, stirring once or twice, until slightly thickened, about 20 minutes. Remove from the heat and cool. Stir in the cilantro. Set aside 4 cups of this sauce. In a medium bowl, stir the remaining sauce into the chicken.
In a medium skillet, warm 1 cup oil. When it is hot but not smoking, fry the tortillas, 1 at a time, turning them once with tongs, until they are flexible; do not allow them to become crisp. Drain the tortillas on paper towels.
Position a rack in the middle of the oven and preheat to 425 degrees F. Lightly coat a rectangular 9 by 13-inch glass baking dish, or any attractive ovenproof serving dish, with nonstick spray or canola oil.
Arrange 8 of the tortillas in an overlapping layer in the bottom of the dish. Spread half the chicken mixture evenly over the tortilla layer. Top with 8 more tortillas, overlapping them as necessary. Sprinkle 1/2 the Monterey Jack and 1/2 the Cheddar over the tortillas. Spread the remaining chicken mixture over the cheese. Arrange the poblanos in a layer over the chicken, overlapping them if necessary. Spread the reserved 4 cups sauce over the poblanos. Arrange the remaining 8 tortillas over the sauce. With a spatula, spread the sour cream over the tortillas. Top with the remaining Jack and Cheddar cheeses.
Bake until the top is lightly browned and the sopa is bubbling, about 45 minutes.
Let rest on a rack about 5 minutes before serving. Serve the sopa hot, topping each portion with a dollop of sour cream and a sprig of cilantro, if desired.
Bring a saucepan of water to a boil. Add the tomatillos and serranos, lower the heat, and simmer until tender, about 10 minutes. Drain and cool in ice water. Core the tomatillos.
In a blender, combine the tomatillos, half of the cilantro leaves, serranos, onions, garlic and 1/2 teaspoon salt. Puree on low speed for 30 seconds. Scrape down the sides of the blender jar and puree again until smooth.
Transfer to a bowl. Finely chop the remaining 3/4 cup cilantro. Stir the cilantro and green onions into the salsa. Adjust the seasoning, adding salt to taste and stirring in up to 1 teaspoon sugar, to taste, if the salsa seems bitter. Use immediately, or refrigerate for up to 3 days.
The sopa can be completely assembled, covered tightly with plastic wrap and refrigerated overnight or frozen for up to 1 month. Thaw the sopa, if frozen, in the refrigerator. Bring the chilled sopa to room temperature before baking.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy The Jimtown Store Cookbook, Jimtown Store, Healdsburg, CA