Step 1

Butter and line a 15-20cm tin with baking parchment. In a large saucepan, melt the butter, sugar, syrup and cocoa. Stir through the biscuits and raisins.

Step 2

Pour the mixture into the prepared tin and press down, then smooth the top with the back of a spoon. Microwave both chocolates in short 20 second bursts, stirring frequently, until melted. Pour them over the mixture in the tin. Use a palette knife or spoon to smooth over, so it's completely coated in chocolate.

Step 3

Put the tin into the fridge and leave for about 2 hrs to set, or overnight. Run a kitchen knife under the hot tap then cut into squares.