Step 1

Set the rack in the middle of the oven and preheat to 350°F. Line a 13 x 9 x 2-inch pan with parchment paper (bring the parchment up the sides of pan so there is a slight overhang) and grease with butter or nonstick cooking spray. (If the parchment is slipping, dot a little butter or nonstick spray in the corners of the pan to help the parchment stick.)

Step 2

Make the brownie batter: Place the butter in a medium microwave-safe bowl and melt in the microwave until bubbling. Add the chocolate and whisk until the chocolate is completely melted. The heat from the butter should be enough to melt the chocolate completely, but if not, place the chocolate-butter mixture in the microwave and heat for 20 seconds or so, then whisk again. (Alternatively, combine the butter and chocolate in a heatproof bowl and set over a pan of simmering water. Stir occasionally until melted.) Whisk in the granulated sugar, brown sugar, vanilla, and salt. The mixture will be a bit grainy; that's okay. Whisk in the eggs. Finally, whisk in the flour until combined. Pour the batter into the prepared pan and spread evenly with a spatula. Set aside.

Step 3

Make the cookie dough: In the bowl of an electric mixer fitted with the paddle or beaters, beat the butter and both sugars for 3 minutes, or until light and fluffy. Scrape down the sides and bottom of the bowl as necessary. Add the vanilla and egg and beat for 1 minute more. Scrape down the sides of the bowl again. Add the salt, baking powder, and baking soda and beat briefly until evenly combined. On low speed, mix in the flour. Finally, add the chocolate chips and mix until just combined.

Step 4

Dollop small spoonfuls of the cookie dough evenly over the brownie batter (no need to spread it out or press it down). Cover the pan with aluminum foil and bake for 20 minutes. Remove the foil and continue baking until the brownie edges are shiny and the cookie portion is golden brown, about 20 minutes more. Transfer the pan to a wire rack and cool completely. To cut, lift the brookies out of the pan using the parchment overhang and transfer them to a cutting board. Pull the parchment away from the edges. Using a sharp knife, cut the brookies into 2-in squares directly on the parchment.

Step 5

Make-Ahead/Freezer-Friendly Instructions: Brookies can be stored in an airtight container at room temperature for up to 3 days; freeze for longer storage.