Preheat oven to 350 degrees Fahrenheit. Line a 9 x 13 dish with parchment paper or you can grease the pan instead.
Mix the flour, white sugar, brown sugar, cocoa, and salt together in a large bowl and set aside.
In a medium-sized bowl beat the eggs. Add the melted butter (but make sure the butter is cooled because if it's too hot it'll cook your egg. Add the vanilla and mix well.
Mix your wet ingredients into your dry ingredients, but just until it's all combined. Don't overmix.
Scoop the brownie batter into the baking dish (it will be thick.) Spread it out with a spatula.
Bake for 28-30 minutes or until a toothpick comes out mostly clean, with a few crumbs attached to it.
While allowing the brownies to cool you can make the cookie dough filling. Cream together the butter, brown sugar, and white sugar.
Add the milk and vanilla and mix again.
Add the flour and mix until all combined.
Fold in the chocolate chips.
Spread the cookie dough mix overtop the brownies with a spatula.
Stick the brownies in the fridge for 20 minutes to firm up that top layer.
Make the glaze by adding the chocolate chips and butter to a saucepan on low-medium setting. Stir often to prevent burning.
Once it's melted transfer the chocolate to a bowl and add the icing sugar and milk and use a handheld mixer to beat for 3-4 minutes.
Put the glaze into piping bag and pipe icing onto brownies, or just spread a thin layer of it on top of the cookie dough layer, whichever you prefer.
Cut and serve!
Notes
For the cookie dough layer you'll want to heat treat the flour. Do this by baking the flour in a thin layer on a baking pan for 10 minutes at 300 degrees, Fahrenheit. You'll want to stir it every 2 minutes.