Prepare 1 box Betty Crocker Dark Chocolate Brownie Mix with the eggs, oil, and water in the amounts listed on its package.

Spread the prepared brownie batter in a greased or parchment-lined 13x18-inch rimmed half-sheet pan. Bake at the package temperature, start checking after 15 minutes, and remove the brownies when a tester has moist crumbs.

Cool the half-sheet pan of brownies completely, then cut enough brownies to make 2 to 3 cups small chunks.

Chill the 2 to 3 cups brownie chunks for at least 30 minutes in the refrigerator, or freeze for 15 minutes, until firm.

Preheat the oven to 350°F. Line 2 baking sheets with parchment paper, or coat them lightly with nonstick spray.

Whisk 3 cups all-purpose flour, 2 teaspoons baking soda, and 1 teaspoon salt together in a medium bowl.

Beat 1 cup room-temperature unsalted butter, 1 cup firmly packed light brown sugar, and 3/4 cup granulated sugar at medium speed until smooth and creamy.

Mix 2 large eggs and 2 teaspoons vanilla extract into the butter mixture on low speed until incorporated.

Gradually mix the 3-cup flour mixture into the wet ingredients just until combined. If the dough is too soft to hold a mound, add 2 to 4 tablespoons additional flour, 1 tablespoon at a time.

Gently fold 2 to 3 cups cold brownie chunks into the cookie dough just until distributed.

Use a 1/4-cup scoop to make 20 large dough portions. Place 6 to 8 portions on each prepared baking sheet with plenty of room between them.

Chill the 20 scooped dough portions for 15 to 30 minutes, or flash-freeze them for 10 minutes, for extra-thick cookies.

Bake 1 sheet at a time at 350°F for 12 to 14 minutes, until the bottoms and edges are lightly browned and the tops feel firm when lightly touched.

Immediately press approximately 1/2 cup chocolate chips, as needed, onto the warm cookie tops. Rest the cookies on the baking sheet for 5 minutes, then transfer them to a wire rack to cool.