Line a 9" round springform baking tin with baking paper.
To a large saucepan add both kinds of chocolate, butter and golden syrup. Melt on a low heat until combined.
Break the digestive biscuits into small bite size pieces and add to the chocolate mixture along with marshmallows and dried cranberries, mix well. (Optional, add any other dried nuts and fruit to the mixture)
Transfer the mixture to the lined baking tin and press down so that it is tightly packed in the tin. Leave to set in the fridge for 3 hours.
Optional topping: Melt the rest of the dairy free milk chocolate and pour over the top of the rocky road, smoothing with a knife. Melt the dairy free white chocolate and drizzle over the top, use a knife to swirl a pattern into the top. Place back in the fridge for an hour to set.
Cut the fridge cake into 12 slices. Store in the fridge.