Preheat oven to 180ºC/160ºC fan-forced. Grease and line a deep 20cm (base measurement) round cake pan with baking paper. Using an electric mixer, beat butter and sugar in a bowl until pale and creamy. Add eggs, one by one, beating well after each addition. Sift flour over butter mixture. Add juice and milk; stir to combine.
Spoon mixture into prepared pan; level surface. Bake for 45 minutes or until a skewer inserted at centre comes out clean. Stand cake in pan for 5 minutes, then turnout onto a wire rack to cool completely.
Meanwhile, to make lemon icing; sift icing sugar into a large bowl. Gradually add juice, stirring until smooth.
Spread lemon icing over cooled cake, allowing it to drip down sides. Serve sprinkled with zest.