In a 9 inch square baking dish, sift flour, salt, baking powder, and cocoa together. Stir in melted margarine and vanilla. Spread the batter evenly in the dish.
In a separate bowl mix topping sugars and cocoa together. Sprinkle this mixture evenly over the batter. Pour the water or coffee over all (don't mix) and bake at 350 degrees for 45 minutes until top springs back when lightly touched.
It's really good served warm with some vanilla soy ice cream or whipped topping. For those of you who have never been exposed to a dessert like this, it should end up being firm on the top and pudding-like on the bottom.