Crush the biscuits to fine crumbs. Melt the butter and stir in the biscuit crumbs. Combine well. Line a spring-form cake tin with greaseproof paper and press the biscuit mixture firmly down into the base to create an even layer.
In a bowl, mix together the yogurt, Philadelphia cream cheese, Tagatesse and lemon zest. Stir well.
Soak the gelatine leaves in cold water. Remove the gelatine leaves from the water, give them a good squeeze and put them in a pan on a low heat. Add the lemon juice to the pan. Stirr until the gelatine has dissolved. Pour the gelatine mixture into the yogurt-cream cheese mixture and stir well.
Spoon the creamy mixture onto the biscuit base and leave to set in the fridge for at least 4 hours.
Blend the slightly thawed raspberries and spread the coulis over the top of the cheesecake and garnish with fresh raspberries.