Melt the butter in a saucepan and then add the flour. Cook for 5 minutes, stirring all the time and making sure not to brown the mixture. Slow whisk in the fish stock and season with salt and pepper. Cook over for 8 to 10 minutes until you have a thick sauce. Remove from the heat and allow to cool.
Peel and thinly slice the shallots. Peel and finely chop the garlic. Pick and chop the coriander leaves, reserving the stalks for later. Peel the prawns and remove the black intestinal tract using the tip of a sharp knife. Season the prawns with salt, pepper and olive oil and set aside.
Clean the mussels under running water and then place in a pan with the white wine, coriander stems and the shallots. Cover and cook over a high heat for 3 minutes. Discard any mussels that do not open. Remove the cooked, open mussels from their shells and set aside.
Heat a frying pan and add a tablespoon of olive oil. Add the squid and cook for 1 minute. Add the garlic, chopped coriander and the sauce. Stir in the mussels.
Preheat the oven to 200'C.
Lay the puff pastry squares flat and spoon the mussels and squid mixture into the centre. Place two prawns on top and then fold the corners of the pastry into the centre and pinch the corners together.
Whisk the egg yolk and then brush into on to the pastry. Place the parcels on a baking sheet, transfer to the oven and bake for 15 to 20 minutes. The pastry should be crisp and golden brown.
Serve the parcels piping hot and with a crunchy salad.
«Prepare the different elements of this dish in advance and simply assemble to when ready to cook and serve.»