Place the chocolate, condensed milk and butter into a large bowl. Microwave on full power in 30 second bursts, stirring frequently until melted. Beat until smooth and then stir in the nuts, berries and marshmallows.
Divide the mixture into 16 small mounds on a parchment lined baking sheet.
Melt the white chocolate in a microwave for 30 seconds to 1 minute. Drizzle over the top of the rocky roads and leave to set. Keep in the refrigerator an airtight container for up to 1 week.