Line your 8 x 8-inch baking pan with parchment paper, ensuring there's an overhang. This will make it easier to lift the cake out later. This initial step is crucial for a clean release.
Scoop out 1 heaping cup of whipped topping from the container and set it aside for later. This will be used as a final layer on the cake.
In a mixing bowl, add both packages of instant vanilla pudding mix. While whisking, gradually pour in 2-1/4 cups of milk. It’s essential to whisk constantly so that the pudding thickens properly.
Continue to whisk for 1 to 2 minutes until the mixture is smooth. The consistency should be thick yet creamy, perfect for layering.
Gently fold in the remaining whipped topping until it's well combined. You want to keep it light and fluffy, so be gentle here.
In a shallow bowl, pour the last 1 cup of milk. Dip each Oreo cookie in the milk, ensuring both sides are soaked but not overly soggy.
Arrange a single layer of the milk-soaked Oreo cookies at the bottom of the prepared baking pan. If needed, break some cookies to fit them perfectly.
Spread half of the pudding mixture over the layer of cookies, creating an even layer. This step is crucial for balancing the flavors.
Add another layer of milk-soaked cookies on top, followed by the rest of the pudding mixture. Finish with a final layer of cookies to create a beautiful cake.
Spread the reserved whipped topping over the top layer of cookies. This adds a lovely finishing touch.
Cover the pan and refrigerate for at least 8 hours, or ideally overnight. This chilling time allows the cookies to soften, creating the cake's signature texture.
Once ready to serve, lift the cake out of the pan using the parchment overhang. Cut it into squares using a sharp knife, wiping the blade between cuts for clean edges. For an extra touch, you can garnish with some crumbled Oreo cookies on top.