Combine first 5 ingredients, stirring until blended; press into bottom and 1 inch up sides of a 10-inch springform pan.
Bake at 350° for 6 minutes; cool.
Beat cottage cheese at medium speed with an electric mixer until smooth. Add cream cheese and next 4 ingredients; beat at medium speed until mixture is smooth. Add eggs, 1 at a time, beating until blended after each addition. Fold in mashed sweet potato, and pour into prepared crust.
Bake at 300° for 1 1/2 hours. Combine sour cream and marmalade, stirring until blended; spread over cheesecake. Bake 10 more minutes; cool on a wire rack. Cover and chill 8 hours. Garnish, if desired.