~- For The Sauce:- Heat The Oven To 350F. Cut salmon into 1/2-inch cubes, and place in a single layer in a medium oven-proof skillet. Sprinkle with salt and pepper and set aside. Sprinkle the gelatin on the cold water to soften, and set aside. Bring the fish stock to a boil. Pour the boiling stock over the salmon in the pan and cook over medium-high heat until the stock returns to a boil. Transfer to the oven and bake, covered with a sheet of buttered parchment or waxed paper, for 1 to 2 minutes. The salmon should remain pink inside. Strain the mixture, reserving the salmon and stock in separate bowls. Melt the butter in a medium saucepan over medium-low heat. Cook the mushrooms and shallots until tender, about 2 minutes. Pour in the brandy, turn the heat to high and light the alcohol with a match. Cook over high heat until the liquid in the pan is reduced by half. Add the reserved stock and reduce again by half. Remove from heat, and stir in the gelatin. Combine the reserved salmon, strained liquid, and Tabasco in a food processor and puree until smooth. Cool refrigerated until room temperature, but do not allow it to set. Whip the cream until stiff peaks form, and fold into the salmon mixture. Pour into a 9-by-5-by-3-inch glass loaf pan, cover with plastic wrap and chill a minimum of 6 hours or as long as 2 days to set the mousse. To make the sauce: Place all ingredients except mayonnaise in a blender and puree until smooth. Transfer to a mixing bowl and stir in mayonnaise. To serve: Run a knife along the inside of the pan. Dip the pan's bottom into hot water for a few seconds. Turn over onto a serving platter. Cut into 1/2-inch slices, and serve with the watercress sauce.