Pick the coriander leaves and set to one side, then finely slice the stalks. Peel and finely chop the onion and garlic, then trim the celery and finely slice.
Place a large saucepan over a medium-low heat and pour in 1 tablespoon of olive oil. Add the onion, garlic, celery and coriander stalks, then sauté for about 10 minutes, or until the veg is softened but not coloured. Meanwhile, shred the chicken and put to one side.
Once the vegetables have softened, add the cumin and cayenne to the pan and fry for 1 minute. Stir in the black beans, along with their liquid, and the chicken stock. Cut the corn kernels from the cob and add it all to the pan, along with the bay leaf. Gently bring it all to the boil, then reduce the heat to low and let it simmer for 15 minutes.
If you prefer your chowder to be on the smooth side, you could blitz it just a little with a stick blender, otherwise just leave it nice and chunky. Stir in the shredded chicken and cream, season with salt and pepper to taste, then return to the hob for a further 10 minutes.
When the chowder is almost ready, toast the corn tortillas in a hot, dry frying pan until lightly golden. Cut them into large pieces, and serve them wedged into bowls of the soup. Cut the lemon into wedges for squeezing over and finish with a sprinkle of the reserved coriander leaves.