Preheat the oven to 350F and spray an 8x8 or 9x9 baking pan with non-stick spray.
In one bowl whisk together 1/2 of the sugar with 1/2 of the cocoa powder.
In another bowl whisk together the flour, baking powder, salt, and remaining sugar and cocoa powder.
Add the milk, butter, egg yolk, and vanilla extract to the flour bowl. Stir until combined with a rubber spatula. The mixture will get quite thick. Fold in the chocolate chips.
Spread the brownie cake mixture into the greased pan as best as possible.
Sprinkle the set aside sugar/cocoa mixture on top of the whole brownie cake batter.
Pour the boiling water on top over as best as you can, but do not stir in.