Line a 20cm square cake tin with plastic wrap, this is going to help you lift the rocky road out later.
Place the shortbread biscuits in a small freezer bag and use a rolling pin to gently crush them into smaller pieces. You can also chop them up roughly. Cut the cream caramels in half so that each piece is about the size of a mini marshmallow. Place the biscuits and toffees into a small bowl along with the pistachios and cranberries.
Place the butter, dark chocolate and syrup in a small saucepan and stir over a low heat until the butter and chocolate have melted and the mixture is smooth. Remove from the heat and add the biscuit mixture. Stir well until everything is completely coated in chocolate.
Tip the contents of the saucepan into your prepared tin. Be sure to scrape all the syrup from the bottom of the saucepan and use it to fill any small gaps. Press the mixture down gently. Cover the tin and leave in the fridge for a few hours until the rocky road has set.
Carefully lift the rocky road out of the tin and peel away the plastic. Cut into 25 squares (a little goes a long way) and pile onto a plate. Dust with icing sugar before serving. Store in an airtight container in the fridge.