In a saucepan, combine the carrot, wine, salt, thyme and parsley. Bring to the boil then turn off the heat and let cool.
Meanwhile, boil the potatoes and mash with 3/4 of the butter. Set aside.
Place the snapper in the wine mixture and bring to the simmer. Simmer 3 minutes. Remove the fish, place on a plate, and strain the liquid. Add the cream to the liquid and reserve.
Melt remaining butter in a saucepan and stir in the flour and nutmeg. Cook, stirring, 2 minutes. Stir in the cream mixture slowly while beating constantly. Simmer, stirring, until thickened, about 5 minutes. Set aside. Preheat oven to 180 degrees C.
Butter a pyrex glass bowl or pie dish and add the cooked fish. Pour over the cream sauce and mix in, breaking up the fish a bit. Top with mashed potato, completely covering the fish.
Sprinkle some nutmeg on top and place the pie in the preheated oven 30 minutes or until potatoes are browning and filling is hot.