Preheat oven to 350 degrees F. Grease a 9 by 13-inch baking pan. Mix all the dry ingredients together in a large bowl. Stir in the oil, buttermilk, and vanilla. Beat in the eggs, one at a time. Stir in the prunes and nuts. Pour batter into prepared pan and bake for 35 to 45 minutes, or until a toothpick inserted in the center comes up clean.
Meanwhile, combine all the topping ingredients in a small saucepan and bring to a boil. Simmer, stirring for 3 minutes. Remove the cake from the oven and place it on a rack to cool slightly. Pierce the cake all over with a wooden skewer. Pour the topping evenly over the cake. Serve warm or cool.
c.1998, M.S. Milliken & S. Feniger, all rights reserved