Preheat the oven to 200C (180C fan oven) mark 6. Put paper cases into 18 0f the holes in two bun tins.
Put flour, baking powder, sugar, butter, eggs, milk and vanilla extract into a mixing bowl and beat with a hand-held electric whisk, or manual whisk until the mixture is pale and very soft. Half-fill each paper case with the cake mixture.
Bake for 10 - 15 minutes until golden. Transfer to a wire rack and leave to cool completely.
Put the icing sugar into a bowl and gradually blend in warm water until the icing is fairly stiff, but spreadable. Add a couple of drops of food colouring if you like.
When the cakes are cold, spread the tops with the icing and decorate. Leave to set, then enjoy!