1 boxed brownie mix, baked according to package directions (I used Ghirardelli Double Chocolate!)*
¾ cup unsalted butter, softened
1 cup brown sugar
¼ cup granulated sugar
2 teaspoon vanilla extract
2 cups all purpose flour
2 teaspoon cornstarch
1 teaspoon baking soda
1 teaspoon salt
1 cup bittersweet chocolate chips
Bake brownie mix according to package directions in an 8×8 pan. Allow to cool, then cut into 25 squares (5 by 5 rows).
Cream butter and sugars until light and fluffy, about 3 minutes. Add in egg and vanilla, beating until combined. Stir in dry ingredients and chocolate chips.
Scoop 1.5 tablespoons of batter and flatten slightly into a thick pancake (see pictures for detail). Take a brownie square and mold it into a disk, then place on top of cookie batter. Scoop another 1.5 tablespoons of batter, flatten slightly, and place on top of brownie disk. Working between your hands, pinch the edges of the cookie batter together and flatten the entire ball of dough slightly more so it is about 3/4 of an inch thick at the center. Place onto parchment paper-lined cookie sheets (you will need 2). Repeat with remaining dough (you will have extra brownies leftover to snack on!). Cover trays with plastic wrap and refrigerate for at least 1 hour, but up to overnight.
Preheat oven to 350°F. Bake cookies for 15 minutes. They will be slightly undercooked, but will continue to cook as they cool. Allow to cool slightly before transferring to a cooling rack. Then eat all the cookies.
*Underbake your brownies. You want them to be fudgy, not cakey!