Pre-heat the oven to 200°c, 180°c for a fan oven or gas mark 6.
Melt the butter in a large saucepan and gently sauté the onion with the bay leaf until the onion is softened but not coloured. Stir in the flour for about 30 seconds before gradually adding the wine, stirring to prevent any floury lumps, before doing the same with the milk. Bring to a simmer and cook for a few minutes until you have a thick sauce.
Cut the broccoli into bite-size pieces and stir into the sauce. Bring to a simmer and cook for about 5 minutes.
Stir in the salmon and prawns, then return to the simmer. Cook for a few minutes, until the prawns are pink, before adding the eggs, dill or parsley, salt and pepper. Spoon into a large ovenproof dish and keep to one side.
To make the topping, boil the potatoes in lightly salted water until tender.
Drain well and then mash with the milk and butter.
Spread the mash over the pie filling. Sit on a baking tray and scatter the cheese over the top. Place in the pre-heated oven for 30-40 minutes until the topping is golden and the filling is bubbling at the edges.
If you are making the pie in advance and storing in the fridge, allow a further 10 minutes cooking time.