Dissolve the coffee in the boiling water.
Beat the remaining cake ingredients in a mixing bowl or a food processor until smooth. Stir in the dissolved coffee. Divide the mixture evenly among the greased and base-lined sections of a 12-hole deep muffin tin and spread the surfaces level.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 12–14 minutes until well risen and the cakes spring back when gently pressed with a fingertip. Leave to cool in the tin for 5 minutes then loosen the edges, turn out on to a wire rack and peel off the lining paper. Leave to cool completely.
Turn each cake the right way up then slice in half horizontally. Whip the cream until softly peaking then use to sandwich the cakes together in pairs and spread the remainder on the tops. Sprinkle with the chocolate curls. These are best eaten on the day they are made.