Potato Topping:
Boil potatoes in lightly salted water. Drain and mash with the butter, milk and Parmesan and season to taste.
Sauce:
Melt butter and sauté the shallot for 5-6 minutes until soft.
Add white wine vinegar and boil for 2-3 minutes until the liquid has evaporated. Stir in the flour to make a roux.
Gradually stir in fish broth and then cook over a medium heat, stirring continuously. Bring to a boil then continue stirring until thickened.
Remove from heat and stir in cream and chopped dill or chives. Season well with salt and pepper as the fish is unseasoned.
Pre-heat oven to 400° F.
Divide fish and peas among four or six mini ramekins (depending on the size) and pour sauce over top. If you have time, allow the fish, pea and sauce filling to cool and solidify. This makes it easier to cover the pie with mashed potato.
Brush potato topping with a little beaten egg.
Bake for 25 minutes until potato crust is golden brown.