Melt the butter in a heated pot and stir in the flour. Cook gently. Gradually whisk in the fish stock and bring to a boil. Stir in the white wine and season with salt and pepper. Reduce heat and simmer gently. In another saucepan, poach the salmon in the cream over low heat about 10 minutes. Drain the cream from the cooked fish and add to the fish sauce. Pour half of the sauce into a bowl and flake the fish into it, removing all the bones. Spoon the mixture into the center of the crepes and fold over. Place on a serving dish and pour the remainder of the sauce over the top. Sprinkle the cheese on top and place under the broiler to brown.