Line a square 8 inch cake tin with tin foil or have a tin foil tray ready for use.
Using a medium sized pan, melt both milk and dark chocolate with the butter and syrup over a gentle heat.
Put the biscuits into a bag crush them with a rolling pin to get big and little-sized pieces.
Take the pan off the heat, and add the crushed biscuits, marshmallows and coconut (and anything else you may like to add). Turn carefully to coat everything with the chocolate mixture.
Tip into prepared tin/tray, smoothing the top as best you can, although it will look bumpy.
Refrigerate until firm enough to cut (about 1–2 hours). Then take the set block of rocky road out of the tin, ready to cut into wedges or bite sized pieces.
Dust the top of the rocky road with icing sugar using a sieve.
Notes
Feel free to add cherries, sweets, nuts or anything else you might have in the cupboard!