Heavily butter 4 pieces of 9 by 12 inch aluminum foil. Then sprinkle with salt and pepper. Preheat oven to 450 degrees. Shred potatoes and mix with lemon
juice and scallions. Make a bed using half the potatoes on each piece of aluminum foil. Place a salmon fillet on the potato bed, sprinkle with salt and pepper and cover with remaining potatoes. Press
down on the potatoes, then enclose tightly in foil. Place in oven for fifteen minutes. Meanwhile, combine shallots, wine, and vinegar in saucepan. Place over medium heat and cook until most of the
liquid is evaporated. Remove from heat and beat in remaining butter. Add salt and white pepper to taste and set aside in a warm place. When it's time to put dinner on the table, heat the broiler.
Unwrap the salmon, and place close to the heat. Brown well, about 2 minutes per side. Arrange the salmon on a platter and serve the sauce separately. Serves 4.