Strictly speaking, this is really a basic Victoria sponge recipe with the addition of sprinkles added to the mix at the end. Piping takes some practice and piping two-tone colours is even harder but there are plenty of tutorials on youtube, There are two methods for two-tone icing, I used the more complicated method of having 2-3 buttercreams coloured with pink and yellow and one plain and then transferred them to the icing bag and piped with a flower nozzle which is quite a cumbersome way of doing it if you're not used to icing. Another easier method is using gel colours piping lines into an icing bag, transferring the buttercream to the icing bag and piping, you'll achieve a ribbon-like effect on the edges of the piped icing - both ways are just as effective and will give a dramatic "wow factor" to the cake.
Preheat oven to gas mark 4/180C and grease 2 20cm sandwich tins and line with greaseproof paper.
Put the butter, sugar and vanilla in a large bowl and using electric whisk, beat until pale and fluffy.
Gradually add the beaten eggs a little at a time, if mix looks like it's curdling, add a tablespoon of the flour.
Sift the flour and baking powder together with a tsp of salt, gradually add to the butter/sugar mix adding 4 tablespoons of milk to the batter.
Sprinkle in the hundreds & thousands and gently fold in, do not over mix.
Divide the mix between the two tins adding a few more sprinkles over the top of the cakes.
Place in the centre of the oven for at least 30 minutes testing with a skewer, it may need another 5 minutes. Test again and if the cake has come away from the tins and the skewer is clean, the cakes are done.
Leave to cool in the tin for 15 minutes before turning out on to a wire rack to cool.
Beat the butter until really soft then add half the sifted icing sugar and vanilla, beat really well.
Continue with the remainder of the icing and the milk to ensure a really creamy icing.
Divide the icing into 2-3 bowls depending on how many colours you're using and add a few drops of colouring to reach the desired richness of colour.
Get a disposable piping bag fitting with a flower nozzle and add the icing a table spoon at a time into the bag as close to the edge of the bag but only half way down the icing bag, continue with the remainder of the icing.
Squeese the icing down and twist the air bag making sure there is no air trapped in bag and twist the end of the bag tight.
Take one of the cakes and pipe individual flower shapes next to each other covering the base of the whole cake. Top with the other cake. Continue piping flowers to the top of the cake re-filling the bag as you go along. Try and stay as neat as possible. When done, gently sprinkle a few more hundreds & thousands over the flowers.
To make piping easier, you can use gel colours making lines of colours along the inside of the piping bag and then gently adding the plain vanilla buttercream in the centre and pushing down and sealing as above. The effect is slightly different but equally pretty.
Food colouring, icing bags and nozzles can be brought from Wiltons CakeCraftshosp or Lakeland. There are tutuorials on Youtube on how to pipe tww-tone icing, this is one like, click on this link.
Above all, follow instructions and you can't really go wrong. One tip that I have, if after taking the cakes out of the tins, the centres look a bit too soft even though the cakes looked baked and skewer was clean, pop them back in the oven with the oven for 5 minutes. The side of the cakes that look uncook facing upwards. I've only ever had to do this a handful of times when making sandwich cakes.