Preheat the oven to 180°C. Melt the butter in a large saucepan and add the leek or onion, celery and Simon Gault Home Cuisine Indian seasoning. Sauté on medium heat for 2–3 minutes until the vegetables are starting to soften. Stir in the flour and cook for a minute or so before adding the warm stock gradually, stirring well to prevent lumps forming. Add half the cream and season with pepper, then fold in the lemon rind and juice and the chopped parsley, and pour the mixture into a buttered baking dish. Scatter the flaked fish over the sauce. Mix the remaining cream into the mashed potatoes and place evenly on top of the fish. Mix breadcrumbs, toasted sesame seeds and grated cheese and sprinkle over. Bake for 40 minutes from cold, or less if mixtures are still warm. Serve sprinkled with chopped parsley. This pie mixture can be made in advance.