Prepare Your Pan and Oven:

1. Position your oven rack in the center and preheat to 350°F (175°C). Line a 9×9-inch baking pan with parchment paper, leaving about 2 inches of overhang on two opposite sides—these will serve as handles for easy brownie removal later. Lightly grease the parchment with butter or non-stick spray to prevent any sticking.

Melt the Butter: 2. Cut the butter into tablespoon-sized pieces and place in a medium saucepan over medium-low heat. Stir occasionally as it melts completely, then remove from heat immediately. Alternatively, melt in the microwave in 30-second intervals, stirring between each interval until fully melted. Let the butter cool for about 5 minutes—it should be warm but not hot enough to scramble the eggs when you add them.

Mix Wet Ingredients: 3. Pour the melted butter into a large mixing bowl. Add both the granulated sugar and brown sugar to the butter, whisking vigorously for about 1-2 minutes until the mixture is smooth, glossy, and well combined. The sugar won’t fully dissolve, but it should be thoroughly incorporated with no butter streaks visible.

Add Eggs and Vanilla: 4. Add the eggs one at a time to the butter-sugar mixture, whisking well after each addition. Make sure each egg is fully incorporated before adding the next one. The mixture should become lighter in color and increase in volume slightly. Add the vanilla extract and whisk until evenly distributed. This vigorous whisking incorporates air that contributes to the crackly top we’re after.

Combine Dry Ingredients: 5. In a separate medium bowl, whisk together the flour, cocoa powder, and salt. For the smoothest brownies, sift the cocoa powder if it’s lumpy. This simple step ensures your brownies won’t have any clumps of cocoa or flour.

Fold Together: 6. Add the dry ingredients to the wet ingredients all at once. Using a rubber spatula, gently fold the mixture together using a figure-eight motion. Mix just until no flour streaks remain—you should see a thick, glossy, uniform brownie batter. Be careful not to overmix; stop as soon as everything is combined. Overmixing develops gluten and creates tough, cakey brownies instead of fudgy ones.

Layer the Batter and Oreos: 7. Pour half of the brownie batter into your prepared pan, spreading it evenly to the edges with your spatula. Arrange 6-8 Oreo cookies on top of this layer in a single layer—they can touch but shouldn’t overlap. You can place them in neat rows or scatter them randomly, depending on your preference.

Add Remaining Batter: 8. Pour the remaining brownie batter over the Oreos, spreading carefully to cover them completely. Use your spatula to smooth the top as evenly as possible. Press 4-7 additional Oreo cookies gently into the top of the batter, creating a decorative pattern. You can leave them whole, break them in half, or quarter them for different visual effects. If using chocolate chips, sprinkle them over the top now.

Bake to Perfection: 9. Place the pan in your preheated oven and bake for 32-37 minutes. The brownies are done when the edges look set and have pulled away slightly from the pan sides, the top has developed that signature shiny, crackly surface, and a toothpick inserted into the center (avoiding Oreos) comes out with a few moist crumbs attached—not wet batter, but not completely clean either. This is the key to fudgy brownies. Start checking at 30 minutes, as oven temperatures vary.

Cool Completely: 10. Remove the pan from the oven and place it on a cooling rack. This is the hardest part—you must let the brownies cool completely in the pan for at least 1 hour, preferably 2 hours. I know it’s tempting to cut into them warm, but brownies continue to set as they cool. Cutting too early will result in a gooey mess (delicious, but messy!). For the cleanest cuts, refrigerate the cooled brownies for 30 minutes before slicing.

Cut and Serve: 11. Once completely cool, use the parchment paper overhang to lift the entire brownie slab out of the pan onto a cutting board. Use a sharp knife to cut into 16 squares (4×4 grid), wiping the knife clean with a damp paper towel between each cut for the neatest edges. For extra-clean cuts, warm your knife under hot water, dry it, then slice—the warm blade cuts through more smoothly.