Preheat the oven to 325F.
Sift the dry ingredients together in a medium bowl and set aside.
Using a hand blender, beat the butter and sugars together until light and creamy.
Whisk the wet ingredients together and add to the butter and sugar, blending until smooth.
Add the flour mix, in batches, beating in until incorporated. You will end up with a large-chunk dough.
Butter or cooking spray a 9x13 pan and press the dough into a flat layer.
Sprinkle the dough with the chocolate chips in an even layer.
Beat the egg whites until stiff peaks form.
Add the brown sugar 1/3 of a cup at a time, beating until smooth.
Drizzle over the chocolate chips as evenly as possible. At this point, I spread out as evenly as possible using a combination of a small spatula and my fingers.
Bake for 30-35 minutes, until the top is hard and sounds hollow when lightly tapped.