Preheat oven to 350˚F and grease a small baking dish.
In a mixing bowl, combine the flour, baking powder, salt, 3 Tablespoons cocoa, ½ cup brown sugar and ¼ cup white sugar in a medium bowl.
In a small bowl or pyrex measuring cup, melt ⅛ cup butter and add the milk and vanilla.
Pour this wet mixture into the dry mixture and combine. This will be quite thick. Turn into the prepared baking dish.
In a small bowl, or even the previously used bowl, prepare the topping by mixing together the brown sugar and cocoa. Sprinkle on top of the fudgy mixture.
Pour the boiling water over the top and place in oven. Bake for 30 minutes. Do not overbake. Cool slightly (15-30 minutes) and serve with ice cream or whipped cream.