Preheat the oven to 200ºC/gas mark 6 and line the tin with the cake cases.
Put all the ingredients except for the milk in the processor and then blitz till smooth. Pulse while adding milk, to make for a soft, dropping consistency, down the funnel. Alternatively put all ingredients into a large mixing bowl and use an electric hand mixer. Or using a bowl and wooden spoon, cream the butter and sugar, beat in the eggs one at a time with a little of the flour. Add the lemon extract and fold in the rest of the flour, adding the milk to get the dropping consistency as before.
Spoon into the cases equally. Put in the oven and bake for 15-20 minutes until the cup cakes are cooked and golden on top, check to see if the cupcakes are ready by inserting a cocktail stick into one of the cupcakes. If it comes out dry then the cupcakes are done. As soon as possible, take the cupcakes in their cases out of the tin and let cool, on a wire rack.
For a simple buttercream icing mix butter with the icing sugar and vanilla essence. Continue to mix until smooth adding the milk to loosen the buttercream.
For Lemon buttercream - make buttercream icing as per the instructions above and add 2 tsp of lemon juice.
Split the buttercream into 4 bowls and using food colouring, colour them pink, blue, green and yellow. Spread the buttercream using a palette knife on top of the cupcakes, creating a small dome and smooth gently with the palette knife. If the buttercream sticks to the knife, heat the knife in a glass of hot water, wipe quickly and smooth the buttercream, repeat if necessary. Don’t worry too much as most of the buttercream will be covered with sprinkles!
Liberally festoon the cupcakes with various glimmer sugars, leaving some plain for contrast. Place randomly on a serving board, to look like a bunch of balloons. Take a little of the unused buttercream and using a freezer bag, half fill with buttercream, seal, then snip off 1/8th of an inch from the corner and pipe ‘strings’ coming from the balloons.