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.
Gradually whisk in the eggs, then sift the flour, cocoa and baking powder. Using a large metal spoon, carefully fold the dry ingredients into the mixture.
Spoon a teaspoon of the mixture into the cake cases, and make a slight indent in the mixture. Spoon a little chocolate spread on top and then cover with the remaining cake mixture. Bake on the middle shelf in the oven for 16-18 minutes until risen, lightly golden and just firm to the touch. Transfer to a wire rack to cool.
For the icing, place the butter in a bowl with the coffee essence and beat until soft. Gradually sift and beat in the icing sugar to make a smooth, creamy icing.
Transfer to a piping bag fitted with a 1cm (½inch) star nozzle and pipe a generous swirl on top of each cake. Decorate with chocolate shapes before serving.