Put your chopped prunes in one of the small bowls, cover with the cup of buttermilk and set aside. In the large bowl add together the oil, sugar, and eggs mixing well with a spoon. In the other bowl combine the flour, soda, salt, cinnamon, cloves, allspice, and nutmeg and use a wire whisk to mix well.
Combine prunes and water in a small saucepan over medium-high heat. Preheat oven to 350 degrees F (175 degrees C). Mix flour, 1 1/2 cups sugar, allspice, baking soda, nutmeg, cinnamon, and salt together in a mixing bowl. Pour batter into prepared pan and bake in preheated oven until a tester comes out clean, about 45 minutes.
Mix flour, 1 1/2 cups sugar, allspice, baking soda, nutmeg, cinnamon, and salt together in a mixing bowl. Combine vegetable oil, 1 cup buttermilk, and eggs in a separate bowl; pour them into the flour mixture. Mix until fully incorporated. Use an electric mixer to blend in the drained prunes; the mixer will break them up a bit.
I used kitchen shears to snip the sticky, dried prunes into small pieces, brought them to a boil in a saucepan with one cup of water and then simmered them for about 10 minutes. They cooked down into a thick sauce which, when cooled, seemed like a perfect jammy consistency to add to this cake.