Line a 30cm x 20cm rectangle tin with baking paper.
Crush the biscuits, either by putting them in a plastic bag and pommeling them with a rolling pin or in the food processor.
Melt the 120g of butter in the microwave or in a small saucepan over low heat.
Mix together the crushed biscuits, coconut and melted butter and press into the tin, making sure it is even. Chill in the fridge to set whilst you make the caramel.
Mix together the condensed milk, butter, sugar and golden syrup in a saucepan over a low heat. Stir for 15 minutes until the mixture becomes a darker golden colour and thick. Do not leave this unattended!
Let the caramel cool slightly before pouring into the tin over your set biscuit base. Return to the fridge.
Melt dark chocolate and butter in microwave or in a small saucepan over low heat (watch like a hawk so that the chocolate doesn’t burn!).
Pour over the caramel and allow to set in the fridge for a few hours before cutting into squares.