First, preheat your oven to 350º F.
Place butter into a 9x13 baking dish and into the oven to melt. Then, remove from the oven and set aside.
Combine the granulated sugar, cocoa powder, self-rising flour, whole milk, and vanilla extract in a mixing bowl. Mix until you have a smooth batter.
Gently spoon the batter over the melted butter in the baking dish; don't stir.
Mix 2 cups of granulated sugar in another bowl with half a cup of unsweetened cocoa powder. Sprinkle over the batter in the baking dish; again, don't stir.
Carefully pour the boiling water over the chocolate topping; again, don't stir.
Place in oven and let it bake for about 35 to 40 minutes. You'll know it's ready when the top looks all set and done, even though the bottom might still be loose.
Once it's out of the oven, let your cobbler cool down for about 15 to 20 minutes.
Optional yet oh-so-wonderful serve with vanilla ice cream. The cool creaminess against the warm cobbler is pure magic.