Line a 2 litre pudding bowl with cling film, leaving some overhanging to cover the top later. Thinly slice the cakes lengthways (8-9 slices per cake) and use the slices to line the base and sides of the bowl, making sure there are no gaps.
Mix the ingredients for the filling with an electric hand whisk until thick and smooth. Fill the lined bowl with it, leaving some space for the rocky road to go on. Set aside.
Break the chocolate for the rocky road into pieces in a heatproof bowl. Add the butter and golden syrup. Set over a pan of simmering water and leave for a few mins until melted – turn the heat off if the water boils, the residual heat will be enough to melt it. Stir until smooth and glossy.
Tip the biscuits into a food bag and crush to a rubble with a rolling pin, creating some fine crumbs and some bigger pieces. Tip into the chocolate mix with the pretzel pieces and marshmallows. Mix until everything is coated in chocolate. Spoon it all over the cheesecake, covering the surface. Wrap the bowl in cling film and place a plate on top with a can to weigh it down. Chill for at least 24 hrs, or up to three days.
Decorate the cheesecake on the day you want to serve it. Heat the cream, chocolate and golden syrup in a pan over a low-medium heat until the chocolate has melted and you have a pourable mixture – don’t let it boil. Unwrap the cheesecake and turn onto a wire rack with a tray underneath. Pour over the chocolate glaze to cover the entire cake. When it stops dripping, use a fish slice to transfer to a plate. Chill until the glaze has set (about 10 mins).
Meanwhile, melt the white chocolate in shorts bursts in the microwave. Drizzle it over the top of the cake, then decorate as you like. We used edible glitter, gold sprinkles and chocolate truffles.