Beat together all the cake ingredients in a bowl until smooth and creamy. Divide the mixture evenly between paper cupcake cases arranged in a 12-hole cupcake tray. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20–25 minutes until risen and just firm to the touch. Transfer to a wire rack to cool.
Make the icing. Melt the chocolate and butter in a heatproof bowl set over a saucepan of gently simmering water (don't let the base of the bowl touch the water). Leave to cool and thicken slightly, then spread over the tops of the cupcakes.
Take a ball of pink icing, about the size of a small cherry, and roll between the palms of your hands until it is about 9 cm (3½ inches) long. Press the icing flat with your fingers, particularly along the top edge, then roll up the icing to make a simple rose shape. Slice off the base and press gently on to a cake. Repeat with the remaining icing until all the cakes are topped with a flower. Serve dusted with icing sugar.