Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper.
In a large bowl, mix together the brownie mix, flour, vegetable oil, eggs, and water until a thick dough forms.
If you want extra flavor, fold in the chocolate chips or chopped nuts.
Scoop about 1 1/2 tablespoons of dough and roll it into balls. Place the dough balls 2 inches apart on the prepared baking sheets.
Bake for 8–10 minutes, or until the edges are set but the centers are soft and slightly underbaked.
Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack.
Serve warm with a cold glass of milk or store them in an airtight container for up to 1 week.