Spray a 9×13 baking pan with cooking spray or line with parchment paper. Preheat the oven to 350º Fahrenheit.
Place the prunes in a small saucepan and cover them with water. Bring to a boil and simmer for about 8 minutes or until they are soft and can be mashed with a fork.
Drain the water, place the prunes on a plate and mash them. They do not have to be totally liquified. It’s ok if there are little chunks.
In a large bowl, mix together the oil, sugar and eggs.
In a medium bowl, whisk together the flour, baking soda, salt, cinnamon, nutmeg and allspice.
Add the flour mixture alternately with the buttermilk, stirring just until combined.
Fold in the pecans and the mashed prunes.
Pour the cake batter into the prepared pan and bake for 25-30 minutes.
While the cake is baking, prepare the buttermilk sauce.
In a small saucepan, combine all of the sauce ingredients. Cook and stir for about 10 minutes over low heat. Keep the heat over low and keep the bubbles simmering on low. Stir just slightly every now and then but don’t scrape the sides of the pan while simmering. The color will be bubbly a creamy butter color. It will start to thicken very slightly into a syrup.
Use a table fork to poke a few holes in the top of the warm cake as soon as it comes out of the oven. Pour the warm glaze over the cake while it is still hot.