Whisk flour, brownie mix, and brown sugar together.
Using a heavy spoon, stir in the eggs, one at a time. Then add the butter and 2 tbsp of water. Batter will be very thick. If the batter seems too dry or that there is too much flour, add 1 more tbsp of water. Fold in the chocolate chunks.
Cover and refridgerate for 2 hours (do not be tempted to skip this step- the cookies will not have the consistency they should).
Preheat oven to 350. Drop by heaping spoonfuls onto a greased cookie sheet. Cookies should be thick to get a real brownie feel, about 3 in apart. Press down slightly, but don't flatten completely. Bake for 8-10 mins.
Remove from oven and allow to sit for 2 mins or so on the cookie sheet before transferring to a cooling rack. Allow to cool completely before transferring to storage.