Put the cake crumbs, butter, cocoa, raspberry jam and rum essence into a food mixer and mix on a medium setting until you have a smooth paste. Leave to rest in the fridge for an hour before rolling. Depending on what cake you use you may need a little more jam to keep it smooth.
Meanwhile, add a few drops of green food colouring paste to the marzipan and work it with your hands until the colour is even.
Roll out the marzipan on a surface lightly dusted with icing/confectioners’ sugar.
Roll out long logs of the cake mixture, approximately 1.5 cm (⅝ in.) in diameter and lay one at a time on top of the marzipan. Roll enough of the marzipan around the cake mixture to cover completely and cut. Set aside seam-side down. Repeat until you have used all of the cake mixture and marzipan, then cut the logs into 6–7-cm (2 ½ –2 ¾ in). pieces.
Dip each end of the logs in the melted chocolate and place on baking parchment. Leave to set in the fridge for 30 minutes before serving.
