18.9 ounce brownie mix - my all-time favorite is Ghirardelli Double Chocolate - this is also a great brownie recipe but I found it more difficult to bake evenly when I made my brownies from scratch
(eggs, oil, and water for brownie mix)
With an electric mixer, cream butter and sugars in a small mixing bowl. Add vanilla and egg; cream again until smooth. Add the flour, baking soda, and salt. Stir gently until incorporated. Stir in chocolate chips. Store in refrigerator until ready to use.
Preheat oven to 350 degrees. Prepare brownie batter as directed. Pour batter into a glass 8x8 or 9x9 baking dish. Scatter pieces of cookie dough over the top of the brownie batter. In my 8x8 square pan, I was able to get about ⅔ of the cookie dough to fit over the brownies and I just saved the rest for regular cookies. Press gently on the dough just until it starts to sink down into the batter a little bit.
Bake for 35-40 minutes (35 for gooey, 40 or more for fully baked), covering with foil if you need to keep the cookies from getting too brown on top. Let stand for 15-20 minutes and cut into pieces for serving.
Beware of taking these out too early because the cookies look brown - usually when I do that, the brownies are still underdone and they sink down in the middle. I found that it was easiest to alternate baking them covered and uncovered. I did the first 20 minutes uncovered, the next 10 minutes covered, and the last 5 minutes uncovered. This allows the brownies to bake without the cookies getting too brown. I've also taken foil and just made a cover around the edges so the middle can bake without burning the tops of the edges.
Recipe by Pinch of Yum at http://pinchofyum.com/chocolate-chip-cookie-brownies