Preheat oven to 350 degrees.
In a medium-sized bowl, whisk together flour, baking powder, salt, sugar, and cocoa powder. Create a well in the dry ingredients and pour in milk, melted butter, and vanilla. Stir together until a thick batter forms.
Pour into a small, ungreased 8-inch rectangular casserole dish with high sides.
In a separate bowl, stir sugar, brown sugar, and cocoa powder together. Sprinkle over the top of the batter evenly.
Pour hot water over the entire thing {WITHOUT STIRRING A THING!}.
Bake for 40 minutes or once the middle is set. {Be sure to place it on a baking sheet in case it bubbles over.} Cool 5-10 minutes before serving.
Serve warm with vanilla ice cream.