Step 1: Prepare Your Baking Pan

Start by preheating your oven according to the instructions on your brownie mix package, typically around 175 to 180 degrees Celsius. Lightly grease a 9×13 inch baking dish or line it with parchment paper to make removal easier later.

Proper preparation at this stage ensures that the dessert does not stick and that the layers bake evenly.

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Step 2: Make the Brownie Batter

Prepare the brownie mix according to the package instructions. This usually involves combining the mix with eggs, oil, and water.

Whisk until smooth and fully combined. Avoid overmixing, as that can lead to a tougher texture. You are aiming for a thick, glossy batter that will bake into a fudgy base.

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Step 3: Assemble the Brownie Base

Pour the prepared brownie batter into your greased or lined baking pan. Spread it evenly using a spatula so the surface is level.

This forms the first layer of your dessert, so take a moment to ensure it is evenly distributed.

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Step 4: Add the Oreo Layer

Place the Oreo cookies directly on top of the brownie batter. Arrange them in a single layer, covering as much surface area as possible without overlapping too much.

Gently press each cookie slightly into the batter so it settles securely but remains visible. This step ensures the cookies stay in place during baking and do not float to the top.

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Step 5: Begin the Cookie Dough Preparation

In a large mixing bowl, add the softened butter, brown sugar, and granulated sugar. Using a hand mixer or stand mixer, cream the mixture together until it becomes light and fluffy.

This process incorporates air into the dough, which helps create a softer texture once baked.

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Step 6: Add Eggs and Vanilla

Add the eggs one at a time, mixing well after each addition. Then pour in the vanilla extract and mix again until everything is fully combined.

The mixture should now appear smooth and slightly creamy.

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Step 7: Combine Dry Ingredients

In a separate bowl, whisk together the flour, baking soda, and salt. This ensures the leavening agent and salt are evenly distributed throughout the dough.

Gradually add the dry ingredients to the wet mixture, mixing until just combined. Avoid overmixing, as this can make the cookie dough dense.

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Step 8: Fold in Chocolate Chips

Add the chocolate chips to the cookie dough and gently fold them in using a spatula. Make sure they are evenly distributed throughout the dough.

This step adds bursts of chocolate flavor to the top layer of the dessert.

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Step 9: Layer the Cookie Dough

Take portions of the cookie dough and gently place them over the Oreo layer. Spread it carefully so it covers most of the surface.

It does not need to be perfectly smooth. Some unevenness actually adds to the rustic appearance and texture.

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Step 10: Bake the Dessert

Place the pan in the preheated oven and bake according to the brownie mix instructions, usually between 30 to 40 minutes.

Check for doneness by inserting a toothpick into the top layer. It should come out mostly clean with a few moist crumbs. Keep in mind that the brownie layer should remain fudgy.

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Step 11: Cool Completely Before Serving

Once baked, remove the pan from the oven and allow it to cool completely at room temperature.

This step is crucial because cutting too early can cause the layers to fall apart. Cooling helps everything set properly.

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Step 12: Slice and Serve

Once fully cooled, slice into squares or rectangles. Use a sharp knife and wipe it clean between cuts for neat edges.

Serve as is or slightly warmed for an extra gooey texture.