Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan and line it with parchment paper, leaving an overhang on two opposite sides for easy removal.
In a large bowl, whisk together the melted butter, granulated sugar, and vanilla extract until the mixture is smooth and well-combined.
Beat the eggs into the butter and sugar mixture one at a time, whisking vigorously after each addition until the batter is thick, glossy, and smooth.
Sift the all-purpose flour, cocoa powder, and salt into the wet ingredients. Use a spatula to gently fold the dry ingredients into the batter until just combined and no streaks of flour remain, being careful not to overmix.
Stir in 1 cup of the chocolate chips, then pour half of the brownie batter into the prepared pan and spread it into an even layer.
Arrange the Oreo cookies in a single layer over the batter, then carefully spread the remaining brownie batter over the cookies, covering them as much as possible.
Sprinkle the remaining 1/2 cup of chocolate chips evenly over the top. Bake for 30-35 minutes, or until the top is set and a toothpick inserted into the center comes out with a few moist crumbs attached.
Allow the brownies to cool completely in the pan set on a wire rack before using the parchment paper to lift them out and cut into squares.