Now I've had Prune Pudding, which is a Manadonese dessert I enjoy at home. But prunes in a chocolate cake. I was hesitant at first, but the credibility of the source diffused all doubt.
From a recipe by David Lebovitz, slightly adapted.

For the prunes:
170 g pitted prunes, diced in small pieces
1/3 cup (80 ml) rum (I used Bacardi gold)
1 tbsp vanilla
1 tbsp sugar

For the cake:
340 g bittersweet chocolate, coarsely chopped
12 tablespoons (170 g) unsalted butter, cubed
6 large eggs, separated
pinch of salt
3 tbsp sugar

Directions:
Prepare the prunes:
1. Simmer the prunes with the rum, vanilla and sugar in a saucepan for a few minutes, until the liquid is absorbed. Remove from heat, and set aside till cooled.

2. Butter a 9-inch (23cm) springform pan. Dust with flour or cocoa powder.
3 In a microwave safe bowl, melt the chocolate and butter, in 30 second bursts, stopping and stirring until smooth.
4. Remove from heat and stir in the prunes and any liquid left in the pan.
5. Stir the egg yolks into the chocolate mixture.

6. Preheat the oven to 325ºF.
7. With a mixer, whip the egg whites with the salt until they begin to hold soft peaks. Continue whipping, adding the 3 tablespoons of sugar, one tablespoon at a time, until the whites hold their shape.

8. Fold one-third of the beaten egg whites into the chocolate mixture thoroughly, then fold in the remaining egg whites just until no streaks of whites are visible. Don’t overfold.

9. Bake for 40 to 45 minutes, or until the sides release a bit, but the center is still soft and moist. Let cool.

Run a thin knife around the cake to loosen it from the pan and remove the springform mold. Dip the knife in very hot water then wipe the blade dry and use it to slice the cake, repeating with each cut.
This cake can be made up to three days in advance, and stored at room temperature. It can also be frozen for up to two months.