Preheat your oven to 350°F (175°C) and line a 9×9-inch square baking pan with parchment paper, leaving a little overhang on the sides for easy removal.

For the brownie layer, whisk together ½ cup melted unsalted butter, 1 cup granulated sugar, 2 large eggs, and 1 teaspoon vanilla extract until the mixture is glossy and smooth. Stir in ⅓ cup unsweetened cocoa powder, ½ cup all-purpose flour, ¼ teaspoon baking powder, and ¼ teaspoon salt until just combined, then spread the batter evenly in your prepared pan.

For the peanut butter filling, mix ¾ cup creamy peanut butter with ¼ cup powdered sugar until smooth. Dollop the mixture over the brownie layer and gently spread it out.

For the cookie layer, cream together ½ cup softened unsalted butter with ½ cup packed brown sugar and ¼ cup granulated sugar until light and fluffy. Beat in 1 large egg and 1 teaspoon vanilla extract, then add 1¼ cups all-purpose flour, ½ teaspoon baking soda, and ¼ teaspoon salt. Fold in 1 cup semi-sweet chocolate chips and carefully spread the cookie dough over the peanut butter filling.

Bake in the preheated oven until the cookie layer turns golden brown and a toothpick inserted into the center comes out with a few moist crumbs. Allow the brookies to cool completely in the pan before cutting into squares.