Grease and line a 9 x 9-inch loose-bottomed square tin with parchment paper.
Chop 400g of the chocolate into small pieces and put into a heatproof bowl along with the butter and golden syrup. Set over a smaller saucepan of simmering water, making sure the bowl doesn't touch the water and melt, stirring every now and then until completely melted and smooth.
Chop the biscuits, or pop them in a freezer bag and bash them with a rolling pin to get big- and little-sized crumbs. You want some pieces to crunch and some sandy rubble. Put these in another large bowl.
Chop the Brazil nuts roughly with a sharp knife and add them to the bowl, along with the cranberries, Maltesers and marshmallows.
Pour over the melted chocolate mixture and mix well, using a wooden spoon.
Once combined, scoop everything into your prepared tin and level the surface as best possible. You will have lumps and bumps as the marshmallows are so big!
Chop the remaining 400g of dark chocolate and place in a clean heatproof bowl over a saucepan of simmering water to melt. Stir every now and then until smooth and glossy.
Pour the melted chocolate over the rocky road, being sure to cover all of the marshmallows sticking out the top, then scatter the mini eggs over.
Place the rocky road in the fridge for at least an hour to firm up.
When it's set and you're ready to serve, take a sharp chef's knife and run it under hot or boiling water. Wipe dry with a teacloth, then cut your rocky road into bars or squares. The hot knife will help avoid your chocolate from cracking or the knife sticking to the marshmallow, and make for a cleaner cut.