Preheat the oven to 350°F and line or grease an 8-by-8-inch square baking pan. Place the prunes in a medium-size bowl. Cover with 2 cups of boiling water and let sit for 10 minutes to soften.
In a small heavy-bottomed sauce pot over medium heat, melt the chocolate with the oil, sugar, and salt, stirring occasionally. Once melted, remove from the heat and stir in the vanilla. Let cool for 5 minutes.
Drain the prunes and place in a blender or food processor along with the cooled melted chocolate mixture. Blend until puréed.
Whisk the eggs in a small bowl. With the blender running on low speed, slowly add the eggs and blend until fully incorporated.
In a large bowl, whisk together the flour, cocoa powder, and baking soda. Stir in the chocolate purée and mix until incorporated. The batter should be quite thick.
Drop the batter into the prepared pan and spread out evenly. Bake for 25 minutes or until set. Let cool in the pan.
