Preheat oven to 150°C (300°F). Place the butter, brown and caster sugars in an electric mixer and beat until pale and creamy. Add the eggs, one at a time, and beat until combined. Add the flour, cocoa and baking powder and mix until combined. Roll tablespoonfuls of the mixture into balls+ and place on baking trays lined with non-stick baking paper, allowing room to spread. Flatten slightly and bake for 15–20 minutes or until light golden. Cool on wire racks.To make the pink marshmallow icing, place the marshmallows and butter in a saucepan over low heat and stir continuously until smooth. Remove from heat, add the chocolate and stir until melted and smooth. Allow to cool completely. Spread half the biscuits with the icing and sandwich with remaining biscuits. Roll the sides of the whoopie pies in the sprinkles to serve. Makes 14.
+ The dough is very sticky, so use damp hands when rolling into balls. The dough results in a soft, cake-like biscuit.