Line a 9x13 baking dish with parchment paper with overlapping sides so you can easily remove the brookes from the pan and cut into squares.
Make box mix brownies per package directions. Pour into the 9x13 baking dish and set aside.
In a separate bowl add softened butter, sugar, brown sugar, egg, and vanilla extract. Using a hand mixer, beat until mixture is light and fluffy. Set aside.
In a separate bowl add flour, baking soda, and salt. Use a whisk to combine.
Add dry mixture to wet ingredients. Use a large spoon to combine. Add chocolate chips and mix together.
Drop spoonfuls of cookie dough over the top of the wet brownie mix.
Bake in the oven at 350 degrees F for 30-35 minutes, or until a toothpick in the center of the brookies comes out clean.
Let cool in the pan 15-20 minutes before serving.
Depending on how hot your oven runs, you may need to cook this recipe for as long as 40 minutes. Unfortunately, you cannot rely on the toothpick test to tell you when the brookies are done because the brownies stay fudgy. Look for the cookies to get golden brown on top and check the edges of the brownies.
Optional: Sprinkle ¼ cup semi-sweet chocolate chips on the top of the brownies when they are done cooking. They will melt down a bit into the brownies while they cool.