Preheat oven to 350°F (175°C). Line a 9×13-inch pan with foil and spray the foil with cooking spray; set the pan aside.

In a large microwave-safe bowl, combine 4 ounces (113 g) coarsely chopped unsweetened baking chocolate and ¾ cup (170 g) unsalted butter. Microwave on HIGH for 2–3 minutes, stirring every 30 seconds, until the chocolate and butter are fully melted and smooth. Let cool slightly (about 1–2 minutes).

Stir 1 ¾ cups (350 g) granulated sugar into the melted chocolate mixture until combined.

Add 3 large eggs one at a time, stirring well after each addition. Stir in 1 teaspoon vanilla extract, ½ teaspoon salt, and 2 tablespoons (10 g) unsweetened cocoa powder until evenly mixed.

Add 1 cup (124 g) all-purpose flour and stir just until combined and no large streaks of flour remain. Spread the brownie batter evenly into the prepared 9×13 pan.

In the bowl of a stand mixer or a large bowl with a hand mixer, cream ½ cup (113 g) unsalted butter and ¾ cup (150 g) granulated sugar together on medium speed until light and fluffy, about 2–3 minutes.

Add 1 large egg, 1 teaspoon vanilla extract, and ½ teaspoon peppermint extract to the creamed butter and sugar; mix until combined.

Add ½ teaspoon baking soda and ½ teaspoon salt; mix briefly to incorporate.

Add 2 cups (248 g) all-purpose flour and mix on low speed (or stir by hand) just until a dough forms. If using, add 8–10 drops green food coloring now and mix until the color is uniform, scraping the sides and bottom of the bowl.

Stir 1 ½ cups (255 g) chocolate chips into the cookie dough.

Using a tablespoon, scoop rounded tablespoons of cookie dough, flatten each slightly with your fingers, and place them evenly over the brownie batter. Press gently so cookie pieces touch and adhere to each other and to the brownie layer; do not try to spread the dough across the batter.

Bake in the preheated oven for 30–40 minutes, until the cookie tops are starting to turn golden and a toothpick inserted in the center comes out with some moist crumbs (not wet batter).

Remove from the oven and cool completely in the pan on a wire rack. Once cool, use the foil to lift the brookies from the pan and cut into bars.

Store cooled brookies in an airtight container for up to 4 days or freeze for up to 3 months.