Preheat your oven to 350 degrees F. Spray or grease a 2-quart baking dish.
Create the base layer: in a large bowl, combine the sugar, flour, cocoa, baking powder, and salt. Whisk to combine. In a small bowl, stir together the buttermilk, water and melted salty butter. Pour the liquid mixture into the flour/cocoa mixture and gently stir, just until well-combined. Spread this mixture into your prepared baking dish.
Create your top layer: In a medium bowl, combine the sugars and cocoa powder. Sprinkle this evenly over the base layer. Combine the vanilla and the boiling water and gently pour this over top. Carefully place your dish in the oven and bake for 30 to 35 minutes, or until it’s mostly set, but still visibly wobbly in the center. Essentially, you want it gooey but not raw – so don’t let it cook to the point of total stiffness.Â
Serve with ice cream or whipped cream, if desired. Â