You will need
Boil the potatoes until soft. Drain immediately.
Mash, preferably through a potato ricer to get an absolutely smooth mixture.
Leave to cool down to touch temperature.
Mix in eggs.
Adjust the oven rack to the middle position and preheat the oven to 180°C.
Butter a medium size ovenproof dish or 6 individual dishes.
In a medium size saucepan, melt the butter, add the sliced leeks, pre-seasoned with Green Onion Seasoning and thyme. Sauté until soft.
Add the wine (if using) and reduce out over high heat.
Bring to the boil while stirring.
Remove from heat and taste for seasoning.
Dish into buttered dish/s.
Sprinkle with parsley.
Pour the sauce over the fish filling.
Spoon potato topping over the filling. Level the top/s.
With a fork make a pattern in the topping or pipe with potato rosettes.
Bake for 30 minutes until golden brown. Can be browned under a grill after 30 minutes if not brown enough.
Serve with a salad.