For the broth, rinse the chicken wings and put them into a large pot with 2.5 litres of water and the salt. Bring to the boil, then skim any scum off the surface with a slotted spoon. Lower the heat, add the rest of the broth ingredients and simmer, partly covered, for about 2 hours, adding an extra 250ml of water half an hour from the end. Taste and adjust the seasoning if necessary to get a flavourful broth. Strain it (keep the chicken for shredding into a taco). Leftover broth can be kept in the fridge to be used elsewhere.
Heat the oil in a wide pot and sauté the onion. When golden, add the garlic and cook until fragrant, then add the tomatoes, bay leaf and chipotle chillies. Add just a little salt for now (about ½ teaspoon) and simmer for about 10 minutes, covered, then remove the bay leaf and blend to smooth – a few bits here and there are fine. Add the caldo de pollo and bring up to a boil, then lower and simmer uncovered for 5 or 10 minutes until it thickens a little. Taste to see if it needs any more salt or other seasoning.
While the sopa is simmering, fry the tortillas. First cut them into strips of about 2cm. Heat a couple of tablespoons of oil in a frying pan and gently fry the strips in batches, turning them over to cook evenly. When golden, remove to a plate lined with paper towel. Scatter with a little salt and turn through. Carry on frying the rest, topping the pan up with a little more oil when necessary.
Serve the soup into bowls. Break up a few tortilla strips per serving andadd to the bowls. Top with crema or sour cream, crumbled cheese and a few avocado slices, and tear in a few coriander leaves. Scatter a little ground chilli over if you want extra heat, and serve with extra tortilla strips and lime on the side.