Preheat the oven to 350 °F
Scatter the berries on the bottom of an 8x8 square baking dish
In a small bowl, stir together 6 tablespoons of the sugar and ¼ cup of the cocoa powder and set it aside.
An a larger bowl, stir together the dry ingredients: the flour, ¾ cup of sugar, ¼ cup of cocoa powder, baking powder and salt
In another bowl, whisk together the wet ingredients - the egg, egg white, canola oil, skim milk and vanilla.
Pour the wet ingredients into the flour mixture and stir with a spatula until well-mixed. Then, pour the whole thing into the baking dish on top of the berries.
Boil 1¼ cups of water and stir the boiling water together with the reserved 6 tablespoons of sugar and ¼ cup cocoa powder. Pour this mixture into the baking dish, right on top of the batter.
Pop the baking dish in the oven for 30 to 35 minutes, or until a toothpick or knife inserted into the center of the cake comes out clean(ish) -- you might end up with a few crumbs because it's a pretty wet and sticky cake, but the cake should look more or less "set" in the middle.
Be sure to store any leftovers in the refrigerator!