Use any 18 ounce boxed brownie mix that includes baking soda in the ingredient list. I used White Lily Chocolate Fudge Brownie Mix with excellent results.
Use parchment paper to line your baking sheet. This will prevent the cookies from sticking and make clean-up easier.
Don't over-mix the dough. Once all the ingredients are combined, stop mixing. Over-mixing can lead to tough, dry cookies.
Use a cookie scoop to ensure evenly sized cookies. This will help them bake evenly and look uniform.
Let the cookies cool on the baking sheet for a few minutes before transferring them to a cooling rack. This will help them set and prevent them from falling apart.
If you want a crispier cookie, bake them for an extra minute or two. Keep in mind that they will continue to cook slightly as they cool on the baking sheet.