To make the shrimp marinade, combine all ingredients in a food processor and blend until chopped and well combined.
Pour over the shrimp, cover and place in the refrigerator to marinate for 30 minutes.
To make herb paste, place all ingredients in a food processor and blend until finely chopped.
Clean all the shellfish. Discard any dead mussels or clams. Soak the clams in cold water for 30 minutes and then scrub clean, then remove the beard of the mussels and scrub clean. Rinse the crab legs and break apart at the joint for smaller pieces.
In a large pot, heat a drizzle of olive oil and then add chorizo and cook until browned.
Add the herb paste and cook for 2 minutes.
Add beer to the pan and bring to a simmer. Cook until the liquid is reduced by half. Then add chicken stock and bring back to a simmer. Add lemon juice and season to taste with salt.
Add the mussels, clams and crab legs to the broth, and place the corn on top. Cook until mussels and clams have opened and crab legs are steamed through, about 10 minutes.
While the seafood cooks, heat a large pan and fry the shrimp until pink and cooked through.
Serve the shellfish and corn in a warmed cast iron pot, with some of the broth, garnished with cilantro sprigs.