Preheat oven to 350 degrees F.
In a medium sized mixing bowl, combine the flour, baking powder, salt, sugar and cocoa. Then stir in the melted butter, milk and vanilla.
Spread the mixture into a greased 1.5 qt casserole dish (or square pan). Set aside.
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. The cake will rise to the top and a pudding will form on the bottom.
Serve warm with ice cream.