In a large bowl, whisk together flour, cocoa, brown sugar, baking powder, baking soda, and salt.
Add the egg whites to your stand mixer or another bowl.
Make a well in the center of the flour and whisk together 3 egg yolks, buttermilk, oil, and vanilla. Gradually incorporate the dry ingredients; don't over-mix. A few dry spots are ok.
Beat the egg whites in your stand mixer or with an electric mixer until soft peaks form. Fold in half of the egg whites (don't over mix! Fold, not stir!)
Add the chopped chocolate and the remaining egg whites and gently fold in until combined.
Heat waffle iron and cook according to directions, making sure to coat the iron with nonstick spray.
Turn your oven on to the warm setting (170 degrees F). Place a baking sheet topped with a cooling rack in the oven, and set the waffles on it to keep warm until ready to serve. (This keeps them from getting soggy.) Cover them with foil if it's going to be a while.
Meanwhile, make the ganache. Add the cream to a microwave-safe bowl. Heat for about a minute and a half, stirring halfway, or until bubbles form on the edges.
Immediately add the chocolate chips and let sit for one minute. Then whisk until all the lumps are gone and the mixture is smooth and creamy. Add the butter and salt. If it returns to room temperature and thickens before you serve it, just throw it in the microwave for a bit until it's liquid again.