Preheat the oven to 350ºF (177 ºC). Butter two 8-ounce (226-g) ramekins. Place the ramekins on a baking sheet. Set aside.
In a large, heat-safe bowl add the chocolate, butter and sugar and melt in the microwave for 10-second increments, stirring in between. Do not overheat your chocolate. You could also use the double-boiler method, see note below.
To a high-speed blender, add the prunes, hot espresso (or water), vanilla and cocoa powder and run on low for 30 seconds to roughly combined. Add in the eggs, salt, baking powder and baking soda and blend for 1 minute, starting on low and working up to high as everything combines. You want the mixture as smooth as possible. Scrape down the sides of the blender and add in the melted chocolate; blend on high for 1 minute more. Pour back into the bowl that you melted the chocolate in. Finally, fold in the flour in as few strokes as possible. Make sure there aren’t any pockets of flour, the mixture will be thick.
Divide evenly between the two prepared ramekins, smooth the tops and bake in the center of the oven for 18 to 22 minutes. 18 minutes will yield a more fudge-like center, whilst 22 minutes will yield firmer cakes. When done, the sides of the cakes will be set and the centers will slightly jiggle.
Let cool for 10 minutes before running a knife around the edges of the cakes and turning out onto plates. Serve with vanilla ice cream, brown sugar caramel and sea salt flakes. Yum.