Prepare the fumet
Keep the fish stock hot in a pot: it must be scalding hot when poured in — cold stock stops the toasting and turns the fideuà starchy. Toast the saffron threads dry for 15 seconds in a small pan, crumble them with your fingers and add them to a ladle of stock.
Sear the seafood
Heat a wide, shallow paellera (36 cm) or a large sauteuse over medium heat with 3 tbsp of olive oil. Sear the prawns 40 seconds per side, lift them out and set aside. Cut the squid into bite-size rings, sear them in the same pan for 2 minutes and lift them out too.
Melt the sofrito for 15 minutes
Add the remaining olive oil (5 tbsp) to the pan, sweat the onion and garlic on low heat (5 minutes, no colour). Stir in the grated tomato and let it reduce gently for 8–10 minutes, until the oil separates at the edge and the mass darkens — that is when the sofrito is ready.
Dry-toast the fideos
Scatter the fideos straight into the finished sofrito and toast them for 3–4 minutes, stirring constantly, until they take on an even light-brown colour and smell of hazelnut. Dry toasting is the heart of fideuà: it gives the pasta bite and aroma and keeps it from turning starchy later.
Fold in pimentón and saffron
Briefly lower the heat, stir in the pimentón — do not brown it, it turns bitter at once. Immediately deglaze with the hot saffron stock, pour in the rest of the fumet, and season with salt and pepper.
Cook in exactly 12 minutes
Cook the fideuà over medium heat, 8 minutes uncovered, without stirring — swirl the pan once if the bubbles gather unevenly. After 8 minutes tuck the mussels, clams and squid evenly into the pan and return the prawns. Cook 4 more minutes: the shells open, the fideos stand up on end at the bottom and the characteristic socarrat crust forms — recognise it by a faint crackling and a warm roasted aroma (do not look in the pan, listen).
Rest
Take the pan off the heat, cover it with a clean kitchen cloth and let it rest for 3 minutes. In that time the aromas deepen and the socarrat sets.
Alioli in the mortar, in parallel
While the fideuà cooks, crush the garlic cloves with a pinch of salt in the mortar until you have a smooth paste. Add the egg yolk and stir with the pestle in one direction until it glows pale yellow. Work in the olive oil drop by drop, stirring constantly, until a thick, creamy emulsion forms (4–5 minutes of handwork). Finish with the lemon juice and taste.
Serve
Serve the fideuà straight from the pan with lemon wedges on the rim of the plate and the alioli in a small bowl on the side. Everyone takes a spoonful of alioli onto their fideuà — the cold, garlicky oil dollop meeting the hot, toasted crust — and that is the moment this dish exists for.
