Clean the mussels by thoroughly scrubbing them under plenty of running water, pulling away the 'beards', the seaweed-like stringy threads. Discard any broken mussels along with the 'beards', and any mussels that don't close tightly when you tap them.
Heat a separate lidded frying pan until hot, add the mussels and half of the white wine; cover with a lid and cook for 1-2 minutes, or until the mussels have opened (discard any mussels that remain closed).
Remove the meat from two-thirds of the mussels and set aside. Reserve the remaining whole mussels. Reserve the cooking liquid.
Heat the oil in a lidded frying pan and fry the leek and carrot for 2-3 minutes, or until softened. Add a splash of water to the pan, cover with a lid and cook for 3-4 minutes, or until tender.
Meanwhile, fry half of the chorizo in a frying pan for two minutes, add the remaining white wine and cook until the volume of the liquid has reduced by two-thirds.
Add the reserved mussel cooking liquid, double cream and half of the lemon juice and bring the mixture to the boil. Stir in the mussel meat, leave to cool slightly and blend the mixture in a blender until smooth.
Pass the sauce through a sieve and add it to the cooked leek and carrot. Add the chickpeas and cod cheeks and simmer for 3-5 minutes. Season, to taste, with the remaining lemon juice and stir in the chopped herbs.
Fry the remaining chorizo in a small frying pan for 2-3 minutes, or until browned.
To serve, ladle the cod cheek mixture into each of four serving bowls. Place the remaining whole mussels and chorizo on top.