In a mixing bowl, mix together the biscuit crumbs and demerara sugar.
Add in the melted butter and mix well. Spoon the biscuit mixture into a 20cm spring-form cake tin, buttered or lined with silicon paper/baking parchment.
Press the biscuit crumbs down firmly and evenly. Put in the fridge until set (approx 20 minutes)
In a large mixing bowl, using a whisk or a wooden spoon, beat together the cream cheese, icing sugar and mixed spice/cinnamon.
Then fold in the double cream and mix well. Crumble the left over Christmas cake over the chilled biscuit base.
Then spoon the creamy mixture over top and smooth the top cheesecake with a palette knife. Chill the cheesecake in the refrigerator for 1 hour until set.