Preheat oven to 190°C bake / 170°C fan bake. Line 2 x 12-hole muffin tins with paper cases.
Beat butter with an electric mixer until smooth. Add Caster Sugar and beat until light and fluffy. Add eggs and mix well.
Sift in the flour, then add milk and vanilla. Beat until smooth.
Divide mixture evenly between paper cases, until they are about 2/3 full (don't overfill or they will form peaks). Bake for 18-20 minutes, until cupcakes are golden, and they spring back when lightly pressed. Turn out onto a wire rack to cool completely.