Using an electric mixer, beat butter, lemon rind and sugar on high speed until pale and creamy. Add eggs, 1 at a time, beating between each addition. Stir in semolina, flour and milk.
Spread mixture into prepared pan. Bake for 45 to 50 minutes or until a skewer inserted into the centre comes out clean.
Meanwhile, make lemon syrup: Place sugar, lemon juice and 1/2 cup cold water in a saucepan over low heat. Cook, stirring, for 5 minutes or until sugar has dissolved. Add lemon slices. Increase heat to high. Bring to the boil. Boil, without stirring, for 4 to 5 minutes or until mixture thickens.
Transfer lemon slices to a plate. Pour half the syrup over cake. Stand for 15 minutes. Turn out on to a plate. Arrange lemon slices over cake. Serve with remaining syrup.
