Preheat oven to moderate; grease two deep 20cm-round cake pans, line bases with baking paper. Make cakes according to directions on packets; divide between prepared pans. Bake in moderate oven about 50 minutes. Stand cakes in pans 5 minutes; turn onto wire racks to cool.

Cut a 12cm-round out of a piece of baking paper; use to cut out spider's head from one of the cakes.

To make butter cream, beat butter in a small bowl with an electric mixer. Gradually beat in half the icing sugar and beat until as white as possible. Add milk and continue beating, then add remaining icing sugar. Beat until a smooth, spreadable consistency. Sift in cocoa powder and mix to combine. Tint with brown colouring; stir in coconut.

Position cakes on a 40cm square prepared cake board. Spread the spider's head and body with butter cream, building up 4 mounds for eyes and pincers, using image as a guide.

Draw 8 legs and 2 pincers on a piece of baking paper. Pipe over markings with melted chocolate. Once chocolate has set, pipe another layer of chocolate over the legs to make them thicker. Repeat once more; leave to set at room temperature.

To make main eyes, attach Smarties to the two extra melts with butter cream and position as shown on mounds. Make a row of five smaller eyes with choc chips and mark centres with red decorating gel.

Position the legs and pincers into butter cream. Make web by cutting licorice into thin pieces and arranging around spider.