In a medium bowl, combine the flour, sugar, 2 tablespoons of the dark cocoa, baking powder and salt. Stir in the milk, oil and vanilla until smooth.
Spread in an ungreased 9 inch square baking pan. Combine the brown sugar and the remaining cocoa; spinkle over batter. Pour hot water over all DO NOT STIR. Bake at 350° for 35 minutes. Serve warm and top with whipped cream or ice cream. Yummy! Enjoy!