Line a 24cm square cake tin with baking paper.
Place the Marie biscuits in a large bowl and crush them with your fingertips or pop them in a large zip-lock bag and gently smash them with a rolling pin until they are fairly evenly crushed although you want some large pieces and some crumbs.
Over low heat gently melt the chocolate, butter and syrup in a saucepan, stirring with a wooden spoon until smooth and glossy. Pour 3/4 of the chocolate over the crushed biscuits and quickly stir through so that the biscuits are well coated in chocolate.
Tip the mixture into the prepared cake tin and flatten with the back of the wooden spoon. Pour the reserved chocolate mixture over the top and smooth with a spatula. Refrigerate the mixture for at least 4 hours or overnight. Using the baking paper remove the whole rocky road and place on a wooden board to serve for dessert. Cut into squares and serve with fresh figs or strawberries or whole bunches of grapes.
If there are any leftovers keep in an airtight container.