Heat a splash of oil in a large pot over a medium heat. Cook the onion, garlic and coriander stalks for 10 minutes with a good pinch of salt to soften and then add the tomatoes, chilli and spices and cook. Stir regularly over a medium to low heat for about 12-15 minutes or until very soft and concentrated. Add the stock and bring to the boil. Add the chicken legs and turn the heat to low. Place the lid on and gently simmer for 45 minutes or until the meat falls off the bone.
Meanwhile, heat about 2 cm of oil in a small frying pan over medium-high heat. When oil is hot but not smoking, add the tortilla strips, in batches, and fry for about 2 minutes, or until golden and crisp. Remove with a slotted spoon and drain on kitchen paper. Sprinkle with a little sea salt and set aside.
When the chicken is cooked, remove from the soup. Remove the meat from the bones and shred into small pieces. Add the chicken to the soup, along with the juice of the lime. Stir through the coriander.
Serve soup topped with tortilla crisps and your choice of accompaniments.
* This is a New Mexican chilli which is traditionally used in tortilla soup – Herbie’s spices does a guajillo chilli which can be found in gourmet supermarkets and delis or ordered online. There are also a number of online stores selling specialty Mexican items which also sell New Mexican chillies. Otherwise substitute whatever dried chillies you can find.