1.Preheat oven to 180°C (160°C fan-forced). Line 12-hole (1/3-cup/80ml) muffin pan with paper cases.
2.Make cake according to directions on packet; pour ¼ cup mixture into each hole. Bake cakes about 20 minutes. Stand cakes in pan 5 minutes; turn, top-side up, onto wire rack to cool.
3.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). 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.
4.Tint half of the butter cream with yellow colouring; spread over five cakes. Tint remaining butter cream with pink colouring; spread over remaining cakes.
5.Using scissors, cut 24 yellow marshmallows and 18 pink marshmallows in half. Squeeze ends of each marshmallow together to form petals. Decorate yellow cakes with six or seven pink marshmallow petals and pink cakes with six or seven yellow marshmallow petals.
6.Position purple Smarties in pink flower centres; position pink Smarties in yellow flower centres. Position flowers on board.
7.On surface dusted with sifted icing sugar, knead icing until smooth. Knead green colouring into icing; divide icing into quarters. Roll one-quarter of the icing into 5mm thick cord. Enclose remaining icing in plastic wrap; reserve. Cut icing cord into three uneven lengths; position on board. Repeat with reserved icing to make 12 stems in total.
8.Pinch stems together near ends; secure bow with a little butter cream. Position spearmint leaves along stems; secure with a little butter cream.
Make sure you have at least one cupcake for each guest. Make the bouquet as large or as small as you like. This is a good cake to take to school for a child’s birthday. A large rectangular plastic tray — readily available in chain stores — is good for a large cake like this. It contains the cake and makes it easy to transport and carry. Secure the cake to the board (or tray) with a little butter cream.