Bring a pot of salted water to the boil over high heat. Add the watercress in batches and blanch until wilted yet still bright green, about 15 seconds. Refresh the watercress in an ice bath, then squeeze out the excess water. In a food processor process the watercress and 3 egg whites and puree until almost smooth. Add the heavy cream and continue to process. Place in a strainer over a bowl (a slight amount will drain out) and puree the scallops in the food processor. Add the remaining egg white, salt and white pepper and continue to process. Add the drained watercress mixture to the scallops and process until well mixed.
Preheat oven to 400ºF.
On a lightly floured surface, roll out 1 piece of the puff pastry into a long rectangle, about 20-inches by 8-inches, or large enough to place the fillet. Place the puff pastry sheet on a large lightly buttered baking. Season both sides of the salmon with salt and white pepper, then place the fillet on the middle of the pastry, skin side down. Spread the watercress mousse evenly over the top of the salmon fillet. Cut the pastry around the salmon to within 2 inches of the fish, leaving a triangular “tail” shape at the bottom and a slightly pointed shape at the “head” end. Brush the edges of the pastry with egg wash.
Roll out the remaining pastry sheet on the floured surface and trim to the same size as the first sheet. Top the salmon fillet with the second pastry sheet and seal the edges to within 3/4-inch of the fish. With a pastry tip, lightly score the top pastry sheet to resemble fish scales, and using the excess pastry, form an eye, mouth and fins. Brush the pastry with the remaining egg wash and bake until golden brown, about 30 – 45 minutes.
Remove from the oven and let the fish rest for 10 minutes before serving.
In a medium saucepan place the shallots, Champagne and fish stock and reduce by two-thirds over high heat. Add the cream to the pan and reduce by half. Remove the pan from the heat and add the butter a bit at a time, whisking constantly, until all the butter has been added. Strain and whisk until the sauce is smooth. Season to taste with salt and white pepper, and fold in the chives. Serve immediately.
Yield: 6 - 8 servings