Put the biscuits in a bowl, pour over the melted spread and mix well. Spoon into a 20cm-round springform cake tin, and press down with the back of a spoon. Cover with cling film and chill the base for 30 minutes.
Meanwhile, put the jelly crystals in a measuring jug, add 250ml of boiling water and the gelatine and stir until dissolved. Leave to cool completely.
Put the cooled jelly in a food processor with the yogurt, vanilla extract, quark and sweetener. Whizz until smooth, then pour over the biscuit base. Cover and chill overnight, or until set.
When ready to serve, melt the chocolate in a heatproof bowl over a pan of gently simmering water, ensuring the bowl doesn’t touch the water (or melt in the microwave on a low heat for 30 seconds). Stir until smooth.
Loosen the edges of the cheesecake using a hot palette knife and transfer to a serving plate. Drizzle with the melted dark chocolate, then dust with the cocoa powder. Cut into 8 wedges to serve.
Give your cheesecake a professional finish by dusting in cocoa powder.
