Preheat the oven to 350 F.
Season the salmon with the salt and pepper. Combine the fish stock, wine, quartered onion, and bouquet garni in a medium-size skillet over medium heat and bring to a gentle boil. Add the salmon and poach until it flakes, 6 to 8 minutes. Remove it from the cooking liquid and let cool to room temperature. Discard the poaching liquid. Flake the salmon into a large mixing bowl.
Heat the olive oil in another skillet over medium heat. Add the chopped onions, season with salt and pepper, and cook, stirring, for 2 minutes. Remove from the heat and add the garlic and parsley. Add to the salmon and mix well. Add the potatoes, egg, and heavy cream and mix again. Season with the salt and pepper and set aside.
Divide the pie dough into equal portions. Lightly dust the work surface with the flour. Roll out each piece into a circle 12 inches in diameter, about 1/8 inch thick. Fold each into fourths so that you can lift it without tearing and use one to line a 10-inch deep-dish pie pan. Spoon the salmon mixture into the pie shell. Place the second crust over the top of the mixture. With a sharp knife, cut away the excess dough. Using your fingers, crimp the edges of the pie firmly to seal completely. With a sharp knife, make several random slashes on the top crust. Bake until golden brown, 25 to 30 minutes. Cool for a few minutes before slicing to serve.
Yield: 8 servings