1. Preheat the oven to 150C.

2. Place vanilla wafers between 2 layers of greaseproof paper. Crush wafers with a rolling pin to yield about 1 1/2 cups crumbs. Combine crumbs, cocoa, sugar and butter in a medium bowl and mix well. Press onto the bottom of a 22cm springform pan. Bake crust in oven for 10 minutes. Maintain oven temperature.

3. Place cream cheese in a large bowl. Beat with an electric mixer on high speed until light and fluffy.

4. Add condensed milk gradually to the cream cheese in the bowl, beating well after each addition. Add chocolate, eggs and vanilla extract and beat well. Spoon mixture over the baked crust.

5. Bake cheesecake until set, about 65 minutes. Let cool to room temperature. Chill in refrigerator for 4 hours or longer. Loosen cheesecake from sides of pan. Remove sides of pan.