Mix together graham cracker crumbs, 1/4 cup sugar, and 1/4 cup melted butter. Press mixture into the bottom of a 9 1/2-inch springform pan. Bake 10 minutes; remove from oven and set aside. Keep the oven on.
Place potatoes in a baking dish. Bake until a knife inserted in center goes through easily, about 1 hour. Cool sweet potatoes enough to handle, peel, and puree.
Beat cream cheese and 3/4 cup plus 2 tablespoons white sugar until smooth. Mix in sour cream, 1/4 cup cream, and 1 1/2 cups sweet potato puree. Beat in eggs one at a time, blending well after each. Pour filling into crust.
Bake in 350 degrees F (175 degrees C ) oven until a tester inserted near the center comes out clean, about 1 hour (center may still be slightly jiggly).
Turn off the oven. Let cake stand 1 hour in oven with door ajar.
Combine brown sugar and 1/4 cup butter or margarine in a heavy small saucepan. Stir over low heat until sugar dissolves. Increase heat, and bring to a boil. Mix in 1/4 cup cream, then nuts. Pour hot topping over cheesecake. Store leftover cheesecake in the refrigerator.
