Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9 inch square pan.
In a medium bowl, mix together the flour, baking powder, salt, sugar, and cocoa. Stir in the milk and melted butter. Spread evenly into the prepared pan.
In a small bowl, combine the brown sugar and cocoa. Spread over the top of the batter in the pan. Pour the hot water over the entire pan of batter.
Bake for 45 minutes in the preheated oven. The cake is done when the cake part is on top and the bottom is of a pudding consistency.
