1.Preheat oven to moderate; grease and line two 18cm-heart pans and line four holes of 12-hole (&1/3;-cup/80ml) muffin pan with paper patty cases. Make cake according to directions on packet, place ¼ cup of the cake mixture into each prepared muffin hole and divide remaining cake mixture between heart pans; bake muffins in moderate oven about 20 minutes and heart cakes about 35 minutes. Stand cakes in pans 5 minutes; turn onto wire racks to cool.
2.On surface dusted with sifted icing sugar, knead 350g of the icing until smooth. Knead yellow colouring into icing; roll until 3mm thick. Using 7.5cm-round cutter, cut four rounds from icing; brush tops of muffins with quarter of the jam, top with rounds of icing. Enclose yellow trimmings in plastic wrap.
3.On surface dusted with sifted icing sugar, knead &1/2; of the icing until smooth. Knead green colouring into icing; roll until 5mm thick. Brush top and sides of one heart cake with a half of the remaining jam. Using rolling pin, lift icing over one heart cake; using sharp-pointed knife, neatly trim excess icing at base of cake. Using hands dusted with icing sugar, gently mould icing around heart cake. Repeat with another 500g of the icing, green colouring, jam and remaining heart cake.
4.Assemble icing-covered muffins and cakes on board to form butterfly.
5.On surface dusted with sifted icing sugar, knead remaining icing until smooth. Divide icing into three portions. Knead orange colouring into one portion of the icing; enclose remaining pieces of icing in plastic wrap. Roll orange icing until 3mm thick. Using cutters or sharp-pointed knife, cut heart and star shapes from icing; position on butterfly wings with a little dab of water. Repeat with reserved yellow trimmings and remaining icing portions, one portion tinted pink and one tinted purple.
6.Position Smarties for eyes on butterfly using a tiny scrap of soft icing. Using scraps of pink icing, shape a small piece into mouth; position on butterfly.
7.Twist tops of chenille sticks into curls; position on cake for antennae.