Line a 20cm, 8” springform tin with nonstick baking paper
Marinade the raisins in the rum
Melt the butterand golden syrup in a heavy based pan then add the biscuit crumbs stir well and then press into the base of the tin. Chill in the fridge whilst you prepare the filling
Melt the chocolate in a bowl over a pan of gently simmering water, remove from the heat and leave to cool slightly.
Whisk the cream until it forms soft peaks, then whisk in the mascarpone and caster sugar until smooth.
Fold the chocolate, nuts and rum raisins into the cream, then spoon on to the base, smooth the top and leave to set in the fridge for 2-3 hours.
Remove from the tin and serve.
For a fancy top - caramelise sugar until golden, then drizzle on nonstick baking paper.
Once set, place on top of the cheesecake