In a large bowl, stir together 3/4 cup sugar, flour, 1/4 cup cocoa powder, baking powder, and salt.
Add milk, butter, and vanilla, stirring until combined.
Spray a 10-inch cast iron skillet with non-stick spray.
Spread batter evenly into the bottom of the skillet.
In a small bowl, stir together remaining 1/2 cup sugar, brown sugar, and remaining 1/4 cup cocoa.
Sprinkle evenly over the batter in the skillet.
Pour the hot water evenly (and carefully) into the skillet. Do not stir.
Bake at 350 degrees for 35-40 minutes, or until center appears set.
Remove from heat, and let stand for 20 minutes before spooning into dishes to serve.
Serve with vanilla ice cream and fresh raspberries.