Soak the shellfish in cold, salted water.
Bring a pan of salted water to the boil and add the pasta shells. Cook for two thirds of the time indicated on the packet and then drain and cool with cold water. Set aside.
Peel and chop the onion. Sweat half in hot olive oil with a pinch of salt but do not allow to brown. Add the shellfish, well-drained and seasoned with thyme, and cover the pan. Leave to cook for 2 minutes and then stir thoroughly. Add the white wine and allow to reduce by half. Remove half of the shellfish and set aside under a wet linen cloth. Add the cream to the pan and cook for a further 2 minutes. Use a pan with a thick base to crush the sticks of lemongrass. Add to the pan with the rest of the onions and cook for a further 2 minutes.
Mix the pasta shells into the sauce and cook over a low heat. When hot, add the reserved shellfish.
Heat a frying pan with olive oil and place the cod skin-side down in the pan. Cook for 1 minute on a high heat. Lower the heat and add a knob of butter and a clove of garlic. Continue cooking for ten minutes and add further knobs of butter throughout the cooking.
Serve the pasta and place the cod on top.
If adding prawns, wash and pan-fry the prawns and place them on top of the pasta.
Season well and serve.
«This recipe can be adapted to other firm, white fish such as snapper or mullet.»