Line baking tray with baking paper, as this will get sticky!

Break biscuits up into crumbs, put into a bowl and add cubed room temperature butter to it. Mix until you get a wet sand look and feel. Line the base of your baking tray with with biscuit mixture. leave aside

For the caramel, store condensed milk, butter and syrup in a saucepan on a medium heat until the butter has melted. Increase heat and bring the mixture to a boil, while always stirring. It will start to thicken and turn a browner colour. Once your happy with consistency, take off heat and continue stirring as it cools down. Don't let it cool completely as it will harden. Just cool enough so it's not molten hot going on top of your biscuit Base. Even out with a spoon.

Place your baking tray into the fridge to cool the caramel down while you do the next step. Melting the chocolate. Cut your dark chocolate into small pieces. This will help it melt quicker and evenly. Boil water in a saucepan and sit your bowl of chocolate over it to melt. Make sure the caramel has hardened enough, before pouring the chocolate over the top and evened out.

Leave in fridge to set. Cut into sqaures when finished. I'd recommend slicing slowly as I cracked the chocolate being to forceful if you want a more straighter look.