Preheat oven to 170C. Line 12-hole cupcake tin with paper fairy cake cases. Using electric beaters, beat together butter and sugar until light and fluffy. Beat in orange zest and egg yolks, then mix in milk until have smooth mixture.
Sift in flour, pinch of salt and baking powder; fold in until combined. In separate, clean bowl, beat egg whites until stiff, then fold into batter. Divide mixture between paper cases and bake for 20-25mins. Leave to cool in tin set on wire rack.
Roll out fondant icing to thickness of £1 coin. Stamp out 7cm circles using biscuit cutter and lay on top of cakes. Decorate with spiders, ghosts, pumpkins or scary faces, using writing icing and liquorice allsorts.