Preheat the oven: Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking pan with cooking spray or line it with parchment paper for easy removal.

Melt the butter and chocolate: In a medium saucepan, melt the unsalted butter and 1 ½ cups of the chocolate chips over low heat. Stir constantly until smooth and fully melted. Remove from the heat and set aside to cool slightly.

Mix the wet ingredients: In a large bowl, beat together the granulated sugar, eggs, and vanilla extract until smooth and well combined.

Add the melted chocolate: Slowly mix the melted chocolate and butter mixture into the egg mixture until fully incorporated.

Combine the dry ingredients: In a separate bowl, whisk together the flour, cocoa powder, and salt. Gradually add this dry mixture into the wet ingredients, stirring until just combined.

Add the remaining chocolate: Fold in the remaining ½ cup of chocolate chips into the batter.

Prepare the Oreos: Break the 24 Oreo cookies in half and gently fold about 18 of the halves into the brownie batter. Save the remaining Oreo halves for topping.

Assemble the brownies: Pour the brownie batter into the prepared pan and spread it evenly. Place the remaining Oreo halves on top of the brownie batter, pressing them slightly into the batter.

Bake the brownies: Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs (not wet batter).

Cool and serve: Allow the brownies to cool in the pan for about 15 minutes before transferring to a wire rack to cool completely. Once cooled, cut into squares and serve.