To make the potato topping, place the potato in a large saucepan and cover with cold water. Cover and bring to the boil. Reduce heat to medium. Cook, partially covered, for 20 minutes or until the potato is very tender.
Meanwhile, to make the filling, heat 40g of the butter in a frying pan over medium-high heat. Add the spring onions and Carrots. Cook, stirring occasionally, for 6 minutes or until the vegetables start to soften. Add the fish and cook, turning occasionally for 1-2 minutes or until lightly browned. Place in bowl
Melt remaining butter in a saucepan over medium heat until foaming. Remove from heat and stir in the flour. Place the pan over medium heat and cook, stirring, for 2 minutes or until the mixture is light golden. Remove from heat. Gradually add the milk, whisking until smooth. Place over medium heat. Cook, stirring, until the sauce boils and thickens. Simmer for 2 minutes. Stir in the cream and cheese. Then add the seafood mixture to the sauce. Stir until well combined.
Preheat oven to 200°C. Line 2 baking trays with non-stick baking paper. Divide the seafood mixture evenly among six 500ml (2-cup) capacity ovenproof freezeproof dishes.
Drain the potato well and return to the pan. . Add the butter and mash until almost smooth. Add the milk and stir until smooth. Use a fork to spread the potato mixture over the pies. Sprinkle with the cheese, breadcrumbs and chopped parsley (optional).
Bake in oven for 20-25 minutes or until light golden. Serve.