Preheat oven to 350 degrees F (175 degrees C ). Mix together graham cracker crumbs, ¼ cup sugar, and ¼ cup melted butter. Press mixture into the bottom of a 9½ inch springform pan
. Bake 10 minutes.Transfer 1½ cups of sweet potato puree to a large bowl. Add cream cheese, scant cup of sugar, sour cream and ¼ cup cream; beat until smooth. Beat in eggs one at a time, blending well after each until creamy. Pour filling into crust.Bake until toothpick inserted in center comes out clean- about 70 minutes. Turn off the oven. Let cake stand 1 hour in oven with door ajar.Combine brown sugar and ¼ cup butter in a small saucepan. Stir over low heat until sugar dissolves. Increase heat, and bring to a boil. Mix in ¼ cup cream, then nuts. Pour hot topping over cheesecake. Refrigerate.