Preheat the oven to 190°C (170°C fan oven, 375°F, gas 5). Line 10 cupcake tins with brown paper cup cake cases. In a mixing bowl, beat the margarine with the sugar until pale and creamy-light in texture. Stir in the vanilla extract.
Gradually whisk in the eggs, then sift the flour, cocoa and baking powder. Add the chocolate chips and using a large metal spoon, carefully fold the dry ingredients into the mixture.
Spoon into the cake cases and bake on the middle shelf in the oven for 16-18 minutes until risen and just firm to the touch. Transfer to a wire rack to cool.
For the icing, sift the icing sugar into a mixing bowl and add the peppermint essence and 20-25ml (4-5tsp) warm water to make a smooth, spreadable icing.
Spread the icing thickly over each cup cake and sprinkle with chocolate strands before the icing begins to set. Allow the icing to set for a few minutes before serving.