step 1
Melt the milk chocolate and dark chocolate in a pot or microwave (be careful not to burn!).
step 2
Once the chocolate has melted and there are no lumps left add the syrup and marshmallows.
step 3
Crush the biscuits in a bag with a rolling pin. This is easier to do if you do small amounts of biscuits at a time. Then add the crushed biscuits to the mixture.
step 4
Put the mixture in a tray which has either been greased or has greaseproof paper in it. Put in the fridge for a few hours to set.