Preheat the oven to 350ºF (177ºC). Line an 8" or 9" square baking pan with foil and spray with nonstick spray. Set aside.
In a medium saucepan over medium heat, melt the butter and chopped chocolate, stirring frequently until completely smooth. Allow to cool for about 15 minutes.
½ cup (113g) unsalted butter, 8 ounces (227g) semi-sweet chocolate
Whisk sugar into cooled chocolate mixture until combined. Add the eggs one at a time, whisking after each addition until smooth. Whisk in the vanilla. Add the flour and salt and stir gently until completely combined.
¾ cup (150g) firmly packed brown sugar, ¼ cup (50g) granulated sugar, 3 large eggs, 1 teaspoon vanilla extract, ¾ cup (90g) all-purpose flour, ¼ teaspoon salt
Add the white chocolate chips and stir to combine. Be sure your mixture isn't too warm, as the chips could start to melt.
¾ cup (128g) white chocolate chips
Pour approximately a third of the batter into prepared pan. Layer 16 Oreos evenly over batter. Pour remaining batter over the Oreos, spreading with a spatula to insure all of the Oreos are covered. Coarsely chop the remaining 8 Oreos and sprinkle evenly over the top of the batter, then press them gently into the batter to secure them into place.
24 Oreos
Bake brownies for 30-34 minutes or until a toothpick or cake tester inserted in the center comes out mostly clean. Allow brownies to cool completely before cutting into squares. Store brownies covered in the refrigerator up to 1 week or in the freezer up to 2 months.
Notes
Semi-sweet chocolate: I always prefer to use chopped bar chocolate, though many readers report that semi-sweet chocolate chips work well, too. Be sure you're melting the chips low and slow so the mixture doesn't seize.
Room temperature eggs: these incorporate into batter much more easily than cold eggs, although this is not absolutely necessary.
Box brownie mix: you can absolutely use a box mix if you prefer.
Double the recipe: double this recipe and bake in a 9" x 13" pan instead. Bake time will be about 36-40 minutes.
All nutritional values are approximate and provided to the reader as a courtesy. Changing ingredients and/or quantities will alter the estimated nutritional calculations.