For the sponge, cream together the butter and caster sugar until soft and fluffy
Add in the eggs and lemon zest and mix well
Fold in the self raising flour
Separate the batter into cupcake cases in a muffin tin and bake at 180C/160C Fan/350F/Gas Mark 4 for 20-25 minutes until golden brown and a skewer inserted comes out clean. Leave to cool completely
To make the buttercream mix together the butter, icing sugar and yellow food colouring until smooth and the desired shade
Pipe the buttercream onto the cupcakes using a piping bag fitted with a closed star nozzle and add desired sprinkles