Pour water and Kahlua into a small heat proof bowl and sprinkle the gelatin over. Stand the bowl in a pan of hot water. Heat gently, stirring until gelatin dissolves. Add to the mixture while machine is on medium speed.
Fold the egg whites in the chocolate mixture. Pour it over the chilled biscuit base and leave to set.
Unmold the cheesecake from the tin and decorate with whippedcream.