red, orange, yellow, green, blue and purple gel food colour
In a large bowl beat together the caster sugar and butter until smooth and creamy.
Beat in the eggs one at a time making sure they are well combined after each addition.
Sift the flour, salt and baking powder and beat until almost combined. Pour in the milk and continue mixing. Scrape down the bowl to make sure everything is incorporated.
Evenly divide the mixture between 3, 7-inch cake tins lined with baking paper and place into a pre-heated oven at 190C for 20 minutes or until a toothpick inserted comes out clean. Turn out onto a wire rack and leave to cool.
For the buttercream sift the icing sugar into a bowl over the butter and beat until sandy. Add the milk and combine.
Beat for a good 5 minutes until the icing is paler in colour and is light and fluffy.
Divide half of the mixture into 6 small bowls and colour each bowl a colour of the rainbow (I have used purple instead of Indigo and Violet). Spoon each colour into its own piping bag.
Colour the remaining buttercream yellow and cover with clingfilm to stop it drying out.
With a sharp knife level off the cooled cakes if needed. Spoon a small dollop of buttercream onto your serving board before placing on the first layer of cake.
Next, take your buttercream and pipe a swirl on the top of the cake starting with red on the outside then orange inside, yellow, green, blue and finally purple in the centre.
Place the next cake on top and repeat with the buttercream. Top with the final cake before placing it in the fridge until the buttercream has set.
Once set take the yellow buttercream and spread it evenly over the whole of the cake. Smooth over with a pallet knife.
For the eyes roll out the black fondant and cut out 2 oval shapes using a cookie cutter. For the mouth roll out a long sausage shape, trim the edges off and use these to create the ends of the smile.
Place the eyes and mouth onto the top of the cake, you may need to secure them with water. Using the remainder of the rainbow buttercream decorate the sides with mini rainbows and finish the face off with a rainbow headband. To create smaller lines I place each piping bag into a new piping bag and cut a smaller hole.