Infuse the chilli, garlic, and oil by heating in a microwave for 1 minute or heating gently in a saucepan for 5 minutes.
Scrub the cockles and mussels, remove the beards, and discard any that do not close when tapped.
Boil the wine, onion, and parsley stalks in a large saucepan, then add shellfish and steam for 4 minutes until opened.
Drain the shellfish, reserve the broth, and remove two-thirds of the cockles and mussels from their shells.
Combine all shellfish in a pan and pour over the reserved broth, leaving behind any gritty residue.
Cook the spaghettini in boiling salted water according to the packet instructions.
Heat the shellfish in the broth with the infused chilli oil and chopped herbs without letting it boil.
Drain the pasta, toss with the seafood mixture, and garnish with the remaining chilli and parsley.