Place the biscuits in a plastic bag and use a rolling pin to bash them into fine crumbs. Alternatively, throw them into a food processor and blitz to crumbs.
Add the chocolate chips to a heat-proof bowl melt over a pan of simmering water. Mix the melted chocolate with the biscuits.
Divide the mixture between 4 pots or rameskins, use a spoon to gently press the mixture down, and refrigerate.
Place the cream cheese and thick double cream into a large bowl and use a hand mixer to beat everything well until it forms stiff peaks.
Reserve a quarter of the mixture for decorating.
Peel and mash the sweet potato, then add it to the cream together with the cinnamon, vanilla sugar and vanilla extract.
Divide the cream cheese between the 4 rameskins and refrigerate for at least 2-3 hours.
Place the remaining cream into a piping bag and decorate each mini cheesecake.
Sprinkle some more cinnamon on top.