Preheat oven to 350F. Butter bottom and sides of 10 cup cake pan, ring mold, or oven proof baking dish. Set aside. In a large bowl, mix mashed potatoes, butter, orange peel, applesauce, salt and milk with a spoon until blended. Mix in eggs yolks and 1/4 cup brown sugar. Beat egg whites until stiff peaks form. Gently fold into sweet potato mixture. Place pecan halves or pieces in bottom of baking dish with tops of halves facing the bottom. Sprinkle with remaining 1/4 cup brown sugar. Spoon sweet potato mixture into dish. Bake until firm, about 30 to 40 minutes. Remove from oven and let stand for 5 minutes before unmolding. To unmold, place serving platter over the top of dish, invert and shake gently to loosen.