Add the saffron threads to a mortar and pestle and lightly bash them to a powder. Add 3 ice cubes, stir to incorporate, and let the bowl sit at room temperature for the ice to melt, around 15 minutes. This will help extract a more vibrant colour from the saffron. Set aside until ready to use.

Preheat a sauce pan over medium heat. Add the olive oil and heat until shimmering. Add the shrimp shells, carrot, celery, onion, garlic and parsley and cook, stirring regularly, until the shrimp shells are golden, around 4 minutes. Add the chicken broth and stir, lifting any brown bits off the bottom of the pot. Add the bay leaves, salt, peppercorns and saffron water. Bring the liquid to a steady simmer, reduce the heat to low, cover with a lid and cook, stirring occasionally, until the broth is golden in colour and flavourful, around 30 minutes. Taste for seasoning and adjust with salt, as desired.

Pour the broth through a sieve into a large pot or bowl. Discard the shells and vegetables. Set the broth aside until ready to use. Leftover broth can be refrigerated in a sealed jar up to 5 days or frozen up to 6 months.

Before cooking, rinse the clams under running water to remove surface dirt, place them in a bowl with fresh water, add 1 teaspoon salt and stir to agitate. Transfer the bowl to the fridge and let the clams sit for around 30 minutes so that they purge any sand inside the shells. Discard any clams that are cracked or open. Scrub the mussels clean under cold water and remove any beards poking through the opening of the shells. Discard any mussels that are cracked or open.

Preheat a large sauté pan or Dutch oven over medium heat. Add the olive oil and heat until shimmering. Add the onion, red pepper, green pepper and jalapeño (if using) and season with a pinch of salt. Cook, stirring, until the vegetables are slightly soft, around 4 minutes. Add the paprika (or achiote) and tomato paste and cook, stirring, around 1 minute. Add the garlic and cook, stirring, until fragrant, around 1 minute. Add the reserved saffron broth, stir to combine and bring to a simmer.

Add the clams and cook until the shells just begin to open, around 6 minutes. Add the mussels and cook until the shells just begin to open around 2 minutes. Add the grouper and cook until the fish is slightly opaque, around 2 minutes. Add the shrimp and cook until the flesh turns pink on the outside and opaque in the middle, around 2 minutes. Taste the soup for seasoning and adjust with salt as desired.

Ladle the soup into individual serving bowls, garnish with chopped cilantro and serve with lime wedges for squeezing and a side of rice or crispy fried plantains, if desired.