Press the crumb mixture into the bottom of a 9 inch round springform baking pan with a circle of non-stick paper at the base. Bake in the oven at 200`c for a few minutes until you mix together the filling. To make the filling, place the cream cheese and ricotta into a bowl and whisk together smooth. Next, add in the remaining filling ingredients and mix together well. Transfer the filling onto the biscuit base and smooth out. Bake in the oven at 160`c for 40 minutes. Remove from the oven and allow to cool down before placing in the fridge to set for 6 hours. When ready, remove out of the tin and place onto a serving plate. Melt together the chocolate with the cream and rum and allow to cool down slightly before pouring over the cheesecake. Decorate the top withsifted icing sugar and serve.