Preheat oven to 450F. and butter a baking dish, 13 by 9 by 2 inches. Prick potatoes and bake on a foil-lined baking sheet in middle of oven until very soft, about 1 1/2 hours. Scoop flesh into a large bowl and mash with butter, sugar, juice, marmalade, gingerroot, and salt. Spread potato mixture evenly in baking dish. Potato mixture may be made 1 day ahead and chilled, covered. Bring potato mixture to room temperature before proceeding. Make topping: In a food processor grind cookies fine. Add butter and pulse motor until mixture resembles soft cookie dough. Wrap topping in wax paper and chill until firm, about 2 hours. Topping may be made 1 day ahead and chilled, covered. Preheat oven to 400F. Crumble topping over potato mixture and bake in middle of oven until topping is browned lightly, about 25 minutes. Serves 8 to 10. Gourmet November 1994