Break each digestive biscuit in half. Divide chocolate bar into 8 equal parts. Place each chocolate piece on top of half of a biscuit.
Divide marshmallows among several long skewers, spacing them far enough apart so that they won’t melt together. Hold the marshmallows over the BBQ and cook over medium heat, turning slowly, until golden brown. Carefully remove marshmallows from skewers and set on top of chocolate pieces. Place the other half of the digestive biscuit on top.