Preheat oven to 350 degrees. Spray an 8x8x2-inch baking dish with cooking spray, set aside.
In a large bowl, stir together flour, baking powder, salt, 3/4 cup granulated sugar and 3 tablespoons cocoa powder. Make a "well" in the center of the flour mixture and pour in milk, melted butter and vanilla, stir until smooth. Spread batter into prepared baking dish.
In a separate bowl, mix 1/2 cup granulated sugar, brown sugar and 4 tablespoons cocoa powder together. Sprinkle over batter. Pour hot water over all of it. DO NOT STIR!
Bake for 35-40 minutes or until the center is set. Let stand 15 minutes. Serve warm with vanilla ice cream.
Cook's Note: You can add 1/2 cup of chopped pecans to the batter if desired.