Make the sauce:
Char the chiles directly on the flames of a gas stovetop with the heat at medium-high (you can do this directly on electric burners as well), turning them with tongs as they blacken until they are blackened all over, 6 to 8 minutes.
Transfer the chiles to a bowl and let stand, covered with a plate or plastic wrap, to loosen the skins, at least 15 minutes. Peel the chiles, then slit them open and remove and discard the seeds, seed pod, and veins. Coarsely chop the chiles.
Cook the onion and garlic in the oil in a large, heavy skillet over medium heat until softened, about 3 minutes. Add the poblanos and the salt and cook, stirring, for 3 minutes. Transfer the mixture to a blender, add the chicken stock or broth and blend until smooth.
Cook the chicken:
Put the chicken in a large bowl and toss with the salt.
Heat a large, heavy skillet over high heat until hot. Add the oil and swirl the pan to coat the bottom. Add the chicken and saute, stirring, until the chicken is just cooked through, 3 to 5 minutes.
Stir the sauce into the chicken and heat through, about 3 minutes.
Make tacos with the accompaniments.
Accompaniments: Warm corn tortillas, grated Monterey Jack cheese or Roasted Corn Salsa (recipe follows).
For the Roasted Corn Salsa:
Bring an inch of water to a boil in a wide pot and add the corn. Cover and cook for 5 minutes. Remove from the water.
Heat a flat griddle or a grill until hot and roast the corn, turning on all sides, until many of the kernels are browned, 6 to 8 minutes total.
When the corn is cool enough to handle, cut the kernels from the cob and mix with the remaining ingredients in a bowl.
Note: The salsa keeps chilled for 2 days.
Yield: About 2 cups
Photograph by Romulo Yanes
Reprinted with permission from Just Tacos by Shelley Wiseman, The Taunton Press copyright (c) 2011