1.Preheat oven to 180°C (160°C fan-forced). Grease and line deep 20cm-round cake pan and deep 18cm-oval cake pan.
2.Make cake according to directions on packet; divide mixture between pans so that both mixtures are the same depth. Bake round cake about 35 minutes and oval cake about 40 minutes. Stand cakes in pans 5 minutes; turn, top-side up, onto wire rack to cool.
3.Assemble cakes on board, using the oval cake for the head and the round cake for the body.
4.To make butter cream; beat butter until white as possible, gradually beat in half the sifted icing sugar then milk, then remaining icing sugar. Beat until smooth.
5.Tint butter cream with green colouring; use a little butter cream to attach oval cake to round cake. Spread remaining butter cream all over cakes.
6.Attach yellow Skittles to Jaffas with a little butter cream for eyes; position on cake. Position one green Skittle for nose; position fruit ring for mouth; sprinkle rainbow choc-chips on cheeks and top of head; position lollipops on head for antennae.
7.Skewer each spearmint leaf with a toothpick; position on sides and top of head. Scatter Cool Fruits and remaining green Skittles on body of alien.
You need a 200g packet of Skittles for Zappo. Oval cake pans can be bought from cake decorating suppliers, or make a cake in a baking dish and cut the oval shape from it – easy and cheaper. Remember to remove the toothpicks out of the reach of children.