Using a food processor (or in a ziplock bag with a rolling pin) crush the cookies into fine crumbs. Place the crumbs into a bowl and add the melted butter. Mix until well combined.
Press the prepared crust onto the bottom of a 23 cm (9 inch) spring form pan. Let the pan sit in the freezer until preparing the cheesecake filling.
In a large mixing bowl beat together cream cheese, sweet potato puree and sugar until homogeneous. Add eggs and mix until smooth. Add vanilla and spices and whisk until combined.
Transfer about half of the filling to another bowl and add the melted chocolate. Mix until the colour is uniform. Pour the chocolate filling into the prepared crust. Pour the rest of the filling on top and smooth with a spatula if needed.
Wrap very well the bottom of the spring form pan in aluminium foil or place it in a bigger pan. It is possible the butter from the crust to leak outside a bit so you need to make sure there won’t be a mess in the oven.
Bake at 160 degrees C for about 1 hour or until the edges of the cheesecake are stable and the centre is just set but still moving a bit. Open the door of the oven and let the cheesecake cool inside for 1 hour.
Remove the pan from the oven and let cool until room temperature. Refrigerate for 4-6 hours before serving.
In a large bowl whip 150 ml heavy cream until stiff peaks form.
In a heatproof bowl combine chocolate and 50 ml heavy cream. Place the bowl over a pan of simmering water. Stir until the chocolate melts and both ingredients are well combined.
Using a rubber spatula carefully fold the chocolate mixture into the whipped cream until uniform and creamy. Refrigerate for 1-2 hours before piping.
To make sweet potato puree: bake the sweet potatoes wrapped in aluminium foil for 1 hour or until soft when tested with a fork. Let them cool and then remove the peel. Puree in a food processor until smooth.