For bottom layer: Heat oven to 350 degrees. Grease bottom of
a 9-inch springform pan. Prepare cake mix as directed on package;
pour half the batter evenly into greased springform pan. Bake 20
(Suggestion: Use extra batter to make
a plain cake in a small round pan, as it wont be needed for
the rest of the recipe.)
For filling: Beat cream cheese, sugar
and vanilla with electric mixer until well blended. Add eggs one
at a time, mixing at low speed after each addition just until blended.
Add in sour cream; pour cream-cheese mixture over cake.
Bake 35 minutes or until center is almost
set. Run knife around rim of pan to separate cake from side of pan.
For topping: Melt chocolate and margarine
over low heat, stirring until smooth. Remove from heat. Add water,
sugar and vanilla; mix well. Spread over cooled cheesecake. Refrigerate
at least 4 hours or overnight.