Line 18 standard muffin cups with paper liners (or use silicone liners like the ones below). Sift the flour and sugar into a mixing bowl. Add the butter, eggs, milk and vanilla. Beat until smooth. Fill the paper liners 3/4 full with the batter.
Bake for 15 minutes or until the cupcakes are golden. Cool on a wire rack.
To make the frosting, mix the confectioners; sugar, cocoa and butter with a little hot water until smooth. Spread over the cupcakes.