Preheat oven to 350 degrees.
In medium bowl, combine 3/4 cup sugar, flour,
3 tablespoons cocoa powder, baking powder and salt.
Blend in milk, melted margarine and vanilla extract until smooth. Pour batter into 8" square pan.
In small bowl, combine remaining 1/2 cup sugar, brown sugar and remaining 4 tablespoons cocoa powder; sprinkle mixture evenly over batter.
Pour hot water over top (I place baking pan on the partially pulled out oven rack for safety): DO NOT STIR. Bake 40 minutes or until center is almost set. Let stand 15 minutes.
Recipe easily doubled by using a 9 x 13" baking pan.