Remove the ice cream from the freezer and leave to stand at room temperature for 30–45 minutes until it is well softened.
Meanwhile, put the crushed biscuits in a bowl, add the melted butter and mix together until the biscuits are moistened. Press the biscuit mixture into a 23 cm (9 inch) round springform tin, pressing it up the edge of the tin to give a 2.5 cm (1 inch) side. Chill in the refrigerator for 20 minutes.
Put the fudge and cream in a saucepan and heat gently, stirring, until the fudge has melted. Carefully spread two-thirds of the fudge mixture over the biscuit case. Spoon the ice cream over the top and level the surface.
Drizzle the remaining caramel over the ice cream with a spoon and freeze for 4 hours. Unmould the cake and serve in wedges.