Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the entire box of brownie mix, eggs, vegetable oil, and flour. Mix with a wooden spoon until a thick, sticky dough forms.
If using chocolate chips or other add-ins, fold them in gently until evenly distributed throughout the dough.
Using a tablespoon or cookie scoop, portion out small balls of dough onto your prepared baking sheet, spacing them about 2 inches apart.
Bake for 8-10 minutes until the edges are just set but centers still look slightly soft and underdone.
Let cookies cool on the baking sheet for 5 minutes to set properly, then transfer to a wire rack.
