Break the biscuits into pieces. The easiest way is to break them by hand, as you can control their sizes. You can also use a chopper, but you have to be careful not to mince them. We must see and feel the biscuits in the cake.
Warm the milk in a preheated pan. Add the cubed butter and let them on low heat until it melts down. Stir from time to time and wait until the butter is completely melted. Then add the sugar and stir again. Once the sugar is melted, add the cocoa and stir well. The hotter the milk, the better will combine with the cocoa.
When the mixture is well combined, turn off the heating and add the raisins. You'll notice the raisins will expand a little bit, that's exactly what we want. Mix well and leave the mixture to cool down for 5 minutes. It mustn't be very hot, but either cold.
Add the mixture over the biscuits and mix well using a spoon.
Add the cubed Turkish delight and rum essence. Mix again. You may also add walnuts or almonds if you like.
Leave aside 10 minutes, for the biscuits to absorb all the liquids.
Line a 900g (9x5in) loaf tin with plastic foil and add the biscuit mixture.
Keep it in the fridge for at least 3 hours before serving, or best overnight. I left mine overnight to harden well.
Once hardened, remove the biscuit cake from the fridge. Remove the plastic foil, slice, and serve.