Preheat oven to 180 degrees C. Lightly grease a 22cm springform pan.
Base: In a small bowl mix together biscuit crumbs, sugar and melted butter. Press onto the bottom and 4cm up the sides of the prepared springform pan.
Bake at 180 degrees C for 10 minutes. Allow to cool. Reduce oven temperature to 165 degrees C.
Filling: In a small saucepan, heat cream and chocolate chips stirring constantly until chips are melted. Remove from heat.
In a large mixing bowl beat cream cheese and sugar until smooth. Add cocoa and beat well. Add eggs and beat on low until just blended. Stir in 1 teaspoon vanilla and reserved chocolate mixture until blended.
Pour over crust. Bake at 165 degrees C for 45 to 50 minutes or until centre is almost set.
Topping: In a small saucepan heat cream and vanilla until just before boiling. Stir constantly and being careful not to boil over.
Place chocolate chips ready in a small bowl. Pour in the hot cream and stir with a spoon until smooth.
Spread over baked cheesecake and refrigerate overnight.