Preheat the oven to 180 deg C.
Mix together the flour, baking powder and caster sugar. Add the butter, eggs, milk and vanilla. Beat until well combined. Spoon the mixture into paper-case lined muffin pans. Bake for about 20 minutes. Leave to cool for 5 minutes and then turn out onto a wire rack to cool completely.
Meanwhile make the buttercream. Beat the butter until soft. Add the icing sugar and combine.
Add the vanilla and milk and beat well until light and fluffy. You could add food coloring too if you''d like colorful cupcakes.
Spread the buttercream onto the cupcakes.