Preheat oven to 325 degrees F. Grease a 2-quart casserole dish and set aside. Place the peeled sweet potatoes in a pan of water and bring to a boil over medium-high heat. Boil for 35 minutes or until tender. Drain the potatoes well and let cool slightly. Place the potatoes in a large mixing bowl with the butter and beat on medium speed with the mixer. Add the sugar, salt, and whiskey and mix well. Spread half the sweet potato mixture in the prepared pan. Sprinkle the sweet potatoes with half of the chopped nuts. Spread the remaining sweet potato mixture on top, then top with the remaining nuts. Place the casserole in the oven and bake at 325 degrees F for 35 minutes or until bubbly in the center. Remove from the oven and serve the drunken sweet potatoes hot.