Line a square tin (20cm x 20cm) tin with parchment paper and set aside.
Chop both the milk and dark chocolate and then put into a pan to melt with the butter and syrup over a gentle heat.
Put the ginger biscuits into a freezer bag and crush them with a rolling pin to get a mix of sandy crumbs and larger pieces of biscuits.
Put the Brazil nuts into another freezer bag and bash them to get different-sized nuts
Take the pan off the heat and add the crushed biscuits and nuts, whole glacé cherries and mini marshmallows. Fold carefully to coat everything with mixture.
Tip the mixture into the lined tray, smoothing the top as much as possible.
Refrigerate until firm enough to cut (roughly 1½–2 hours). Then take the set block of rocky road out of the lined tray ready to cut.
Push the icing sugar through a small sieve to dust the top of the Rocky Road, then with the long side in front of you, cut into it 6 slices down and 4 across, so that you have 12 squares.