Sift the flour and salt and set aside. Cut up the butter or margarine and place in a warm mixing bowl. Add the sugar and beat until light and fluffy. Lightly mix the eggs and lemon rind and gradually beat into the creamed mixture. This should be done in several additions: if added too quickly the egg will not be absorbed by the fat and a curdled mixture will result. If necessary add a little of the flour with the last few additions of egg. Using a metal spoon, fold in the remaining flour half at a time.
Divide the mixture evenly between two greased and lined
Cream the butter for the filling and gradually beat in the sieved icing sugar. Use to sandwich the two cake layers. Warm the strained lemon juice for the icing and sieve the icing sugar into a mixing basin. Gradually beat in sufficient lemon juice to make a smooth coating consistency. Pour the icing over the top of the cake and spread evenly. Warming the liquid for mixing encourages the icing to set more quickly.