Place the butter and soft light brown sugar in a mixing bowl. Beat until pale and creamy.
Add the eggs, milk and vanilla. Beat again to combine.
Add the self-raising flour, baking powder, cinnamon and ginger and fold everything together.
Add the finely chopped stem ginger and gently fold through.
Line a muffin tray with paper cases and place a gingernut biscuit in each one.
Spoon the batter evenly into the cases.
Bake for approximately 20 minutes until risen and firm.
Transfer to a wire rack to cool completely.
Make the frosting
Put the icing sugar, butter, cinnamon, ginger, vanilla and milk in a large bowl. Whisk until you have a light, fluffy frosting.
Transfer the frosting to a piping bag.
Pipe tall swirls on top of each of the cupcakes.
To finish, crumble the gingernut biscuit over the cakes.
It's best to keep these cupcakes covered in a cool, shaded place or in the fridge as they have a liberal topping of ginger buttercream frosting. Keep your cupcakes in sealed container in a single layer so as not to squash the frosting.