Pour into greased and paper-lined pan. Bake for 45 minutes or until done. When cool, ice with mocha butter icing. Add water to make up the amount if necessary. Add evaporated milk.
Dice prunes finely.
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.