Preheat the oven to 325 degrees F. Line an 8x8 baking pan with parchment paper. Leave about 2 inches of overhang to make it easier to remove the pudding from the pan once it's done.
Add the prunes (no need to chop them up), butter, vegetable oil, water, brown sugar, milk powder, cocoa powder, espresso powder, and semi-sweet chocolate to a saucepan over medium low heat. Warm everything together until the butter and chocolate are melted and the mixture is glossy and smooth. Remove from heat and stir in baking soda. Let the mixture sit (off of the heat) for about 15 minutes so that the prunes soften and soak up all that chocolatey flavor. 1 cup Prunes1/2 cup Salted Butter1/4 cup Vegetable Oil1 cup Water1 1/4 cups Brown Sugar2 tbsp Milk Powder1/2 cup Cocoa Powder2 oz Semi-Sweet Chocolate 1 tsp Espresso Powder1 tsp Baking Soda
Pour the prune mixture into a food processor or blender and blend into a smooth paste. The mixture may be thick, do not add additional water.
In a large bowl, add vanilla extract, eggs, and buttermilk. Whisk together until combined, about 1 minute, then pour the pureed prune mixture in. Whisk until combined and add the dry ingredients - flour, baking powder, and kosher salt. Pro tip: Mix until just combined and no patches of flour remain, we want this pudding soft and tender. 1 tbsp Vanilla Extract3 large Eggs1/2 cup + 2 tbsp Buttermilk2 cups All Purpose Flour2 tsp Baking Powder1 tsp Kosher Salt
Pour the batter into a prepared baking dish and bake for 70-80 minutes (mine took 75 minutes) until a toothpick inserted in the center comes out with a few moist crumbs. Do not bake until the toothpick comes out clean, the pudding will be dry.
While the pudding bakes, make the sauce by warming butter, brown sugar, heavy cream, cocoa powder, chocolate, and a pinch of salt over medium low heat in a medium saucepan. Simmer for about 10 minutes, until the sauce is smooth and pourable. Remove from heat and stir in vanilla extract and allow it to cool until the cake is finished. 3/4 cup Salted Butter1 cup Brown Sugar 1 1/2 cups Heavy Cream2 tbsp Cocoa Powder2 oz Semi-Sweet Chocolate
Once the pudding comes out of the oven, let it sit for about 10 minutes to cool just slightly. This also allows it to firm up a bit so that it doesn't turn to mush when you pour the sauce on top. Use a wooden skewer to poke a holes over the top of the cake (be generous here - poke lots of holes! and poke all the way down to the bottom of the pan so that the chocolate sauce can seep all the way down).
Pour just enough sauce on top to coat the top of the cake. Let it seep in for about 2-3 minutes, then pour again. I like to do this 3-4 times. You will have leftover sauce - sauce this for serving with a nice dollop of vanilla ice cream!