Line 10 sections of a 12-section bun tray with paper cake cases. Put the biscuits in a polythene bag and bash with a rolling pin to break up.
Mix the biscuit pieces with the white and milk chocolate in a bowl.
Put the plain chocolate in a heatproof bowl with the milk, butter and golden syrup. Set the bowl over a saucepan of very gently simmering water and leave until the chocolate and butter have melted, stirring frequently until smooth. Leave until cool but not beginning to set.
Tip in the biscuits and chopped chocolate and mix until coated in the melted chocolate mixture. Divide the mixture between the paper cases and leave to set. If liked, decorate with chocolate curls and put in ramekins before serving.