Preheat oven to 325.
Butter and flour 10 inch springform pan.

Cheesecake batter:
In food processor, blend sour cream, vanilla sugar, eggs and vanilla for one minute.
Add cubed cream cheese ( 1 inch cubes ) and blend till smooth.
Pour 2 Tbs melted butter in feed tube while running.
Set aside.

Carrot cake batter:
In mixer, beat oil and sugars until smooth.
Add the eggs and vanilla and beat until the mixture is light and creamy.
Stir in the flour, baking soda, cinnamon, allspice and salt until just combined.
Mix in the carrots and walnuts.

Assemble:
Spread half of the carrot cake batter into the prepared pan.
Pour half of the cheesecake batter over the cake batter.
Repeat.

Bake:
Bake the cheesecake for about 60-90 minutes.
The cheesecake should still be slightly jiggly in the center when it is finished baking,
Run a knife around the outside of the pan and let cool completely in the pan on a wire rack for about an hour.

Frosting:
Mix together the butter and cream cheese until smooth.
Add the powdered sugar and mix until no lumps remain.
Add the vanilla and mix well.
When the cheesecake is cool, spread on top of the cheesecake.
Cover the cheesecake with tin foil or plastic wrap, careful not to touch the frosting, and refrigerate until well chilled, at least 6 hours.
Serve cold.
The cheesecake can be refrigerated for 2 - 3 days.