Melt the butter/palmin in a saucepan over medium heat.
Once the butter/palmin is completely melted, turn off the heat and add the chocolate and cocoa powder. Stir until the chocolate is completely melted and you have a smooth mixture.
While the chocolate mixture briefly cools, whisk together the powdered sugar and egg in a separate heat-proof bowl or saucepan.
Next, add the chocolate to the egg mixture. Pour in slowly and continually whisk so that the egg doesn't curdle/cook.
Let the mixture cool for 5 minutes. Meanwhile, line a loaf pan with cling film - make sure it covers everything so that the chocolate doesn't leak out!
Now, it's time to layer the cookies and chocolate. Start with the chocolate mixture on the bottom, then add cookies, then chocolate, cookies, and continue until you run out of chocolate. The number of layers you get will depend on the size of your loaf pan, but we usually get at least 4-5 layers of cookies!
Put the loaf tin in the fridge to set for at least 2 hours (the longer the better, overnight works best!).
Once fully set, you can slice and enjoy! Tip: if you want clean slices, take the cake out of the fridge and leave it at room temperature for 20-30 minutes before slicing!