1. Preheat oven to 140°C.

2. For the crust, in a small bowl combine the butter with the chocolate wafer crumbs.

3. Press into the bottom of a buttered 10-inch spring-form pan. Bake for 10 minutes. Remove from the oven and cool on rack.

4. For the filling, in a large bowl beat the cream cheese until very smooth on the low speed of an electric mixer. Gradually add the sugar.

5. Add the eggs, one at a time. To ensure that the batter has no lumps and that no ingredients are stuck to the bottom of the bowl, stop the mixer several times and scrape down the sides of the bowl with a rubber spatula.

6. Stir in the heavy cream and the vanilla. Pour the batter into the prepared pan and set the pan on a baking sheet.

7. For the swirl, in a small saucepan bring the heavy cream to a simmer over high heat.

8. Add the chocolate to the pan and turn the heat down to low.

9. Stir constantly until chocolate is completely melted. Remove from heat and cool slightly.

10. Drop this mixture by the teaspoonful onto top of batter.

11. Using the tip of a sharp knife, swirl chocolate mixture into batter forming a decorative pattern.

12. Bake until edges are set and center moves only slightly when pan is shaken, about 1 hour.

13. At the end of the baking time, turn heat off and using a wooden spoon to keep oven door slightly ajar, cool cake in oven for 1 hour before removing.

14. Cover and refrigerate for at least 12 hours.

15. Remove cake from refrigerator at least 15-30 minutes before cutting and serve.