Put the crushed biscuits in a bowl and stir in the melted butter.
Tip the biscuit mix into the bottom of a large, greased springform tin. Press down firmly all over, then pop in the fridge to firm up while you make the filling.
Melt the chocolate and set aside to cool a bit.
Put the double cream in a large bowl. Whisk until very thick but before it turns buttery.
Add the cream cheese and sifted icing sugar and fold together gently.
Add the Baileys and fold through.
Add the chocolate and fold through. Since the filling is cold, the chocolate will form creamy speckles in the mixture, which looks great and tastes amazing.
Spoon the filling onto the biscuit base and smooth over the surface. Refrigerate overnight.
Once set, run a warm knife around the inside of the tin before unclipping, then remove the cheesecake.
Sift cocoa powder over the top, then transfer to a stand, board or plate.