Place the white chocolate melts into a heatproof bowl. Microwave on Medium/50% power, stirring every minute until they are fully melted.
Spoon the melted chocolate into a sealable plastic bag and snip one corner of the bag to make a piping bag. Pipe enough white chocolate on top of the biscuits, allow to drip down the side to resemble custard flowing over the pudding.
Place a Jaffa on top and a small spearmint leaf each side of the Jaffa and secure in the melted chocolate.