1.Preheat oven to 150°C/300°F. Grease deep 20cm(8-inch) square cake pan; line base and sides with baking paper, extending paper 5cm (2 inches) above sides.
2.Make cake according to directions on packet. Spread mixture into pan; bake about 35 minutes. Stand cake in pan 5 minutes before turning, top-side up, onto wire rack to cool.
3.Knead ready-made icing on surface dusted with a little sifted icing sugar until icing loses its stickiness. Roll out about one-third of the icing between sheets of baking paper into a 3mm (⅛-inch) thickness; cut out two 2.5cm (1-inch) circles for eyes. Tint some of the icing scraps yellow, roll out between baking paper; using pattern from pattern sheet, cut out beak. Tint remaining icing pale blue, roll between sheets of baking paper; using pattern, cut out eyes.
4.Tint scraps and remaining icing a darker shade of blue, roll between sheets of baking paper; cut out 1cm (½-inch) circles for pupils of eyes. Using pattern from pattern sheet, cut out wings from remaining icing.
5.To make butter cream, beat the butter (and any flavouring, if using) in a small narrow bowl with an electric mixer until the butter is as white as possible (this will result in a whiter butter cream which will give you better results if colouring it).
6.Gradually beat in half the sifted icing sugar then the milk, then the remaining icing sugar. Beat until the butter cream is smooth and spreadable. Keep scraping down the side of the bowl during beating. Tint butter cream yellow.
7.Level top of cake; turn, cut-side down. Using pattern, cut out owl shape. Secure cake on 30cm(12-inch) square cake board with a little butter cream.
8.Reserve 2 tablespoons of butter cream, spread remaining butter cream all over cake.
9.Using picture as a guide, position cut-out pieces of icing for eyes, beak and wings to cake (dab the backs of each piece with a tiny bit of water to help secure them together).
10.Fill piping bag with reserved butter cream, snip end from bag, pipe tacking stitches on wings, as pictured. Position bullets to form feet.
EQUIPMENT: deep 20cm(8-inch) square cake pan; 30cm(12-inch) square cake board; small paper piping bag. Apart from piping the tacking stitches, the cake can be completed a day ahead of the party. We positioned the owl on a larger cake board decorated with a paper cut-out tree.