Peel and devein 8 prawns and cut into 1.5cm pieces. Leave the remaining prawns unpeeled. Set aside.
To clean the squid, use one hand to hold the hood (body) and, with your other hand, reach under the hood and grip the head and tentacles. Pull them gently from the body and discard. Peel off the flaps and remove mottled skin from the hoods. Remove plastic-like quill from inside the bodies. Rinse hoods well, cut in half lengthways and cut into 1cm-wide pieces.
Use a sharp knife to cut a shallow cross in the base of each tomato. Place the tomatoes in a heatproof bowl, cover with boiling water and stand for 5 minutes. Remove from the water. Carefully remove skins, and halve, deseed and dice the tomatoes. Set aside.
Combine stock and saffron in a medium saucepan. Bring to the boil over high heat. Boil, covered with a tight-fitting lid, for 10 minutes. Reduce heat to low, cover, and hold at a gentle simmer.
Heat 1 tablespoon of the oil in a 24cm (base measurement) non-stick paella pan over medium-high heat. Add the whole prawns and cook, turning occasionally, for 3 minutes or until they turn pink. Transfer to a plate and set aside. Add the fish to the pan and cook, turning once, for 1 minute each side or until lightly browned. Transfer to the plate with the prawns.
Heat remaining oil in the pan over low heat. Add the onion and cook, stirring occasionally, for 3 minutes or until onion is soft. Do not brown.
Add tomatoes, rice, paprika, salt, chopped prawns and squid. Mix well, pushing any rice around edge gently into mixture, and pat down. Gently pour over 6 ladlesful (about 750ml/3 cups) of the hot stock, and cook, uncovered, over high heat for 5 minutes. Do not stir. Reduce heat to medium and simmer, uncovered, for 10 minutes. Add fish, mussels and peas, and push mussels, seam-side down, gently into mixture.
Continue to add stock and test the rice as in step 5 of the basic paella valenciana recipe (p 50). Cook for a further 15 minutes. Top with whole cooked prawns. Cook for a further 5 minutes. Remove from heat and cover with 2 clean tea towels. Set aside for 10 minutes before serving.
