Line an 8” square baking tray with greaseproof paper. Place the butter, golden syrup and Cocoa Powder in a pan over a low heat and stir until melted.
Break the chocolate into pieces and leave to one side. Once the mixture has melted in the pan remove from the heat and pour in the chocolate, stir the chocolate through the mixture until melted. – if it doesn’t completely melt place over the pan back over a low heat until the chocolate has melted.
Add the biscuits and raisins into the melted chocolate mixture and stir until coated.
Pour the mixture into the prepared tin and using a spatula or back of a spoon smooth out to cover the base of the tin.
Break the chocolate into pieces and place in a microwaveable bowl. Melt the chocolate in the microwave in 30 second bursts, stirring between each burst until the chocolate is melted.
Pour the melted chocolate over the tiffin base and smooth out to evenly cover the top of the tiffin. Place the tiffin in the fridge to set for a couple of hours.