To a frying pan, over high heat, add one tablespoon of olive oil and quickly sear the salmon, then the prawns, then the mussels in batches until almost-done, don’t cook through, as they’ll continue to cook in the pies. Keep the oily seafood juices in the pan and transfer the seafood to a colander.
To the same pan, add another tablespoon of olive oil, heat, then turn the heat down to medium, then cook the diced onion until soft. Add the asparagus pieces and diced zucchini and continue to fry until tender.
Add the cooking cream and simmer for a few minutes, stirring occasionally, then gradually add the sifted flour, stirring continuously, to create a thick sauce.
Turn the heat to low, then add the cheeses, spring onions, fresh dill, peas, salt and pepper, stir well to combine, then taste, adjust the seasoning if necessary, then remove from the heat to cool a little.
Turn your attention to the seafood: chop the prawns in half or thirds, depending on their size, then chop the salmon into chunky pieces around 1 ½ cm in length.
Transfer half of the salmon to the creamy spring vegetable sauce, mash roughly, stir to combine, then taste and adjust seasoning if needed. Set aside to cool.
Preheat your oven to 220°C/430°F. Grease 4 ovenproof pie dishes (12.5cm/5in wide x 4cm/1.5in deep) with butter and space them out evenly on a rimmed baking tray.
Distribute the creamy seafood and spring vegetable mix into each pie dish, filling two thirds of each dish, then pop the salmon pieces, prawns and mussels on top, pressing then down into mixture a little, then top with more of the creamy vegetable mixture to fill the pie dishes.
Top each dish with a sheet of pastry, pressing the pastry around the edges to seal, allowing any excess to overhang, then use a fork to prick the centre of each top, and use a pastry brush to brush the whisked egg on the pastry lid.
Bake for 15-20 minutes or so until the pie lids are golden, then serve immediately with garden salad.