Place the butter, sugar, eggs, sour cream, lemon juice and rind in a bowl and whisk to combine. Add the flour and baking powder and whisk until smooth. Spoon into 2 x well greased 4 cup capacity (1 liter) Bundt tins and bake for 40-45 minutes or until cooked when tested with a skewer. Cool in tins for 10 minutes. Turn out onto a wire rack to cool completely.
To make the lemon icing, place icing sugar, juice and water in a bowl and mix to combine. Spoon over cakes to serve. Serves 8-10