Preheat oven to 350 degrees F.
In a medium-sized mixing bowl, combine the flour, baking powder, salt, sugar, and cocoa.
Stir in the melted butter, milk, and vanilla.
Spread the mixture into a greased 1.5 qt casserole dish (or square pan).
In another bowl, combine the dry topping ingredients (sugar, brown sugar, salt, and cocoa).
Sprinkle on top of the batter; do not stir.
Pour the boiling water on top; do not stir.
Bake for 30 minutes, or until the top of the cake is almost set.
Serve warm with ice cream.