Pre-heat oven to 180C/350F.
In a medium bowl combine flour, sugar, 3 tablespoon of the baking cocoa, baking powder and salt. Stir in the soy milk, oil and vanilla until smooth. Spread in an ungreased 23 centimeter square baking pan. Combine the brown sugar and the remaining 3 tablespoon of cocoa and sprinkle this over the top of the batter in the cake pan. Pour the hot water over and do not stir. Bake for 35 to 40 minutes. Serve warm.
I mix and bake in the same dish (circular pyrex) except for the brown sugar/cocoa mixture which I mix in a measuring cup. Upside - one less dish to wash. Downside - one less bowl to lick. It should come out like a brownie on top and with hot fudge sauce below. Enjoy!