Cook prunes in water for 15 minutes until soft. Drain and set aside 1/4 cup of the prune liquid. Add water to make up the amount if necessary. Add evaporated milk. Dice prunes finely. Reserve 1/2 cup for icing. Set aside. Heat oven to about 180°C.
Cream butter until soft. Add sugar gradually while continuously beating until light and fluffy. Add eggs in three stages, beating well after each addition.
Fold in vanilla and prunes. Sift flour, salt and baking powder and add alternately with milk and prune liquid.
Blend well after each addition. Pour into pan lined with greased paper. Bake for an hour or until done. Frost with icing as given.
To make prune icing: Mix milk, sugar and vanilla. Chill. Cream butter until soft. Add milk and sugar mixture little by little while continuously beating until icing becomes smooth and of spreading consistency. Fold in prunes.