Preheat oven to 300 degrees.Cover prunes with water. Bring to a boil and cook until soft and mashable, about eight minutes. Remove from heat, drain water, and mash on a plate. Set aside.Mix together oil, sugar, and eggs. In a separate bowl, sift together dry ingredients. Combine wet and dry ingredients, add buttermilk and vanilla and stir gently until just combined. Throw in the mashed prunes and stir gently to combine. DO NOT OVERMIX!Pour batter into buttered baking dish (9 x 13 or so) and bake for 35 to 40 minutes. DO NOT OVERBAKE OR INY WILL PADDLE YOUR BOTTOM.While cake has five minutes remaining, make the icing:Combine all icing ingredients in a medium saucepan over medium heat and bring to a slow boil. Boil without stirring for 5 to 7 minutes, or until icing starts to turn dark. Do NOT allow icing to reach soft ball stage; icing should be caramel in color, but not sticky like caramel. Icing should be easily pourable.Remove cake from oven and pour on icing immediately.Allow to rest on the counter. Serve warm.NOTE: There is absolutely zero “prune effect” associated with this cake. The end.