Soak prunes. Place the chopped prunes in a heatproof bowl and cover with boiling water. Let soak 20 minutes, then drain.
Prep. Heat oven to 300°F and grease a 10-inch round baking pan with cooking spray. Cover bottom with a piece of parchment paper and grease that as well.
Mix wet ingredients. Combine oil, buttermilk, sugar, eggs, and almond extract in a large mixing bowl. Whisk until smooth.
Mix dry ingredients. Combine flour, espresso, cinnamon, baking soda, cloves, and salt in a separate medium bowl. Whisk to break up any lumps.
Combine. Add the dry ingredients to the wet ingredients and stir with a rubber spatula until just combined. Fold in the prunes being careful to not overmix.
Bake. Scrape the mixture into the prepared pan and bake for 60 minutes or until springy and a toothpick inserted in the middle comes out with a few moist crumbs still attached.
Stir icing. Make the icing while the cake is baking. Whisk together powdered sugar, buttermilk, and orange zest in a large bowl until smooth. The icing should be very thick so it doesn't run off the cake but still thin enough to drizzle. Start with 5 tablespoons of buttermilk, then add another tablespoon if necessary.
Decorate. Let cake cool 15 minutes then run a knife around the edge of the cake pan and flip cake onto a plate or cake stand. Drizzle with icing and serve warm or room temperature.