Method:
1 Pre heat the oven to 200°C fan forced.
2 Combine the flour, cocoa, baking powder and bicarbonate soda in a medium bowl.
2 Using an electric mixer, beat butter and sugar until fluffy, beat in the egg, vanilla and sour cream, stir in the dry ingredients.
3 Line a baking tray with baking paper and spoon tablespoons of mixture onto the tray, bake for 7-8 minutes, cool.
4 Place the marshmallows in a bowl with 1 teaspoon of warm water, microwave on medium heat for 20 seconds, stir until smooth, working quickly, spread across the base of a biscuit and sandwich together with another biscuit, repeat with remaining biscuits.
5 Arrange on a plate with a drizzle of marshmallow and mint sprigs if desired.