• Preheat the oven to 180°C (fan). Line a cupcake baking tin with 12 cases.
• Beat the margarine (or butter) and caster sugar together until light and creamy.
• Mix in the eggs one at a time, adding a spoonful of the flour with each egg to stop the mixture from curdling.
• Add the remaining flour, milk and vanilla extract, and fold everything together into a smooth cake mixture. Now fold in the rainbow sprinkles.
• Spoon the mixture into the cupcake cases, filling each one roughly two-thirds full.
• Bake for 18-20 minutes until risen and a toothpick inserted into the middle comes out clean. Transfer to a wire cooling rack and leave to cool completely.

Now make the buttercream

• In a large bowl beat the butter until really soft and pale in colour. Sift in the icing sugar and mix until smooth, then fold in the vanilla extract and milk.
• Mix in a few drops of pink food colouring until you reach the desired colour.
• Spoon the buttercream into a piping bag fitted with a large, open-star nozzle. Pipe tall swirls of buttercream on top of the cupcakes and decorate with more sprinkles to add a pop of colour.