Heat oven to 350 degrees.
In medium mixing bowl, combine ¾ c. sugar, flour, 3 T. cocoa, baking powder and salt. Blend in milk, melted butter and vanilla; beat until smooth. Pour batter into square 8 x 8 or 9 x 9 inch pan.
In small bowl combine remaining ½ c. sugar, brown sugar and remaining 4 T. cocoa; sprinkle mixture evenly over batter. Pour hot water over top; do not stir.
Bake 40 minutes or until center is almost set. Let stand 15 minutes; spoon into dessert dishes, spooning sauce from bottom of pan over top. Garnish as desired.