Crush the biscuits and mix with the cocoa and melted butter or margarine. Press into a tin with removable rim.
Soak the sheets of gelatine in plenty of water for 5 minutes.
Melt the chocolate in a saucepan together with the milk. Squeeze the excess water out of the sheets of gelatine and dissolve them in the warm mixture.
Whisk the eggs and sugar until fluffy. Add the fromage frais. Stir the egg mixture into the chocolate mixture after it has cooled but before it sets. Pour into the tin. Refrigerate.
Soak the sheets of gelatine for the topping in plenty of cold water for 5 minutes.
Dissolve the instant coffee powder and brown sugar in boiling water. Squeeze the excess water out of the sheets of gelatine and dissolve them in the coffee. Add the Kahlua. Allow to cool. Pour the coffee mixture over the cheesecake. Refrigerate.