Line a 12-hole muffin tin with paper cake cases.
Put the butter, sugar, flour, eggs and vanilla extract in a bowl and beat with a hand-held electric whisk until smooth and creamy. Divide among the cases.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes, or until risen and just firm to the touch. Transfer to a wire rack to cool.
Make the buttercream by beating together the butter and sugar in a bowl until smooth and creamy. Remove one cooled cake from its case and take a thick, angled slice off the top, and discard. Spread a little of the buttercream over another cake, position the slice on top and spread with buttercream to make a large 'face'.
Spread a large, rectangular board with 4 tablespoons of the buttercream and scatter with the grated chocolate. Spread the remaining buttercream over the cakes, then position in a snaking line over the chocolate, with the face cake at the front.
Roll out the pink or red icing thinly on a surface lightly dusted with icing sugar and cut out 9 rounds using a 5 cm (2 inch) cookie cutter. Place on all the cakes except the face and end cakes. Cut out a pointed tail from the trimmings and place on the end cake.
Roll out the chocolate icing and cut out a round using a slightly larger cutter. Position on the face cake. Then cut out 10 x 2.5 cm (1 inch) rounds. Place on the rest of the cakes and top each with a candy-covered chocolate sweet. Shape and position some eyes and a mouth with the icing trimmings and remaining sweets.