Combine 1 cup oil, 1 cup sugar, and 3 eggs. In a separate bowl, sift together 1 ½ cups flour, 1 teaspoons soda, 1 teaspoon nutmeg, 1 teaspoon allspice, and 1 teaspoon cinnamon. Combine wet and dry ingredients, add 1 cup buttermilk and 1 teaspoon vanilla and stir gently until just combined. Add mashed prunes and stir gently Pour batter into buttered baking dish and bake for 35 to 40 minutes. When cake has five minutes remaining, make the icing