In a large pan cook the unpeeled sweet potatoes in just enough water to cover completely. Bring to a boil, cover, and cook until tender, about 35 minutes. Drain and cool, then peel off the skins. Ina mixing bowl mash the potatoes with the butter. Add the sugar, salt, and whiskey.
In a buttered 1 1/2 quart round casserole dish, spread half of the potatoes and sprinkle with half of the pecans. Repeat the layers. Bake at 325 degrees until hot, about 30 minutes.
NOTE: White sugar may be substituted for brown sugar to give a different taste to the dish.