**Prepare the pan**
Line a 9x9-inch square pan with parchment paper, leaving some overhang for easy removal.
**Melt the chocolate mixture**
In a saucepan over low heat (or microwave-safe bowl), combine the milk chocolate, dark chocolate, butter, and golden syrup. Heat gently, stirring frequently, until melted and smooth. Let cool slightly.
**Combine dry ingredients**
In a large mixing bowl, combine the crushed biscuits, mini marshmallows, and most of the Maltesers (reserve a handful for topping).
**Mix with chocolate**
Pour the melted chocolate mixture over the dry ingredients. Stir until everything is well coated.
**Assemble**
Transfer the mixture into the prepared pan. Press it down gently with a spatula to ensure an even layer. Sprinkle the reserved Maltesers on top, pressing them lightly into the surface.
**Chill**
Refrigerate for at least 2 hours, or until firm.
**Cut and serve**
Once set, lift the rocky road out of the pan using the parchment paper. Cut into squares or bars. Serve chilled or at room temperature.