Preheat oven to 375°F.
Lay out liners in cupcake pan.
Cream butter and caster sugar together until pale and fluffy.
Whisk egg using a fork.
Add half of the egg into sugar/butter mixture. Beat until uniform.
Add remaining egg and vanilla extract. Mix until uniform.
Fold half of the sifted flour into batter.
Add milk and remaining flour. Fold until well combined.
Divide batter between cupcake cavities and bake for 12 minutes or until risen and golden on the top.
Allow to cool for 10 minutes on a rack before removing from the tin.