Make the chicken
Put the chicken pieces and backbone in an 8-quart, heavy-duty pot. Add enough water to cover the chicken by 3 inches. Add the onion, celery, garlic, 2 Tbs. salt, and 1/2 tsp. pepper. Bring to a boil over high heat, lower the heat to medium, and continue to boil, uncovered, for 30 minutes, skimming off any foam that forms on top.
Using a slotted spoon, remove the chicken pieces from the pot and place on a rimmed baking sheet to cool. When cool enough to handle, remove the chicken from the bone and shred the meat with your fingers or 2 forks. Discard the bones, strain the broth through a medium-mesh strainer, and reserve for another use.
Make the tomato sauce
Put the tomatoes in a blender and blend until puréed.
Heat the oil in a 12-inch skillet over medium heat. Add the onion and bell pepper and cook, stirring often, until beginning to soften, 3 to 5 minutes. Add the puréed tomatoes, garlic powder, cumin, 2 tsp. salt, and 1/2 tsp. pepper to the skillet and bring to a gentle boil over medium heat. Reduce the heat to low and simmer, stirring occasionally, for about 45 minutes.
Add the shredded chicken to the tomato sauce and heat until warmed through, stirring occasionally. Taste and adjust the seasoning, if necessary.
Make the tacos
Combine the masa harina, salt, and 2-1⁄4 cups warm water in a large bowl and stir until a dough forms. Divide the dough into 12 pieces and shape each into a ball. Using a tortilla press or rolling pin, flatten a ball into a 6-inch disk, transfer it to a plate lined with plastic wrap, and cover with another sheet of plastic wrap. Repeat with the remaining balls of dough.
Pour the oil into a 7- to 8-quart Dutch oven and heat over medium-high heat until a deep-fry thermometer registers 350°F. Place 1 tortilla in the oil. When it begins to puff, press the end of a metal spatula into the middle of the tortilla so that it bends into a taco shape; hold the spatula in place until the taco is golden brown and crisp, 1-1⁄2 to 2 minutes. Transfer the taco to paper towels to drain, and repeat with the remaining tortillas.
Fill each taco shell with some of the chicken mixture. Top with lettuce, tomatoes, and salsa, if using, and serve right away.
Photo: Scott Phillips
Recipe adapted from Moveable Feast with Fine Cooking.