Preheat the oven to 350 degrees Fahrenheit. 

Place 24 whole Oreo cookies into a food processor, pulsing until the cookies are a crumb-like consistency. You should end up with 2 cups of crumbs to make the Oreo cookie crust.

Mix cookie crumbs and melted butter until the butter is evenly distributed and all of the cookie crumbs are coated. The crumbs will appear wet.

Pour the Oreo crust mixture into a prepared 9×9 pan. You can use butter, cooking spray, or parchment paper to keep the bars from sticking to the baking pan.

Press the crust mixture into the bottom of the pan so that the entire area is covered and the mixture is evenly distributed. Using a spoon, press down on the crushed Oreos to ensure that the crumbs are tightly packed.

Bake at 350 degrees for 8 minutes.

Remove the crust from the oven and set it aside, leaving the oven set at 350 degrees.

Begin preparing the filling by putting the cream cheese and sugar in a large bowl. Beat on medium speed with an electric or stand mixer until the mixture is smooth and creamy.

Mix in the eggs and vanilla extract.

Once the cream cheese mixture is well combined, add the marshmallow fluff and continue to mix. 

Chop the remaining Oreos and fold into the cheesecake batter until they are well incorporated.

Pour the batter over the crust, using a flexible spatula to scrape the bowl and spread the batter evenly. 

Bake for 20 minutes. Then, without opening the oven, reduce the heat to 200 degrees and bake for an additional 30 minutes. 

Once the baking is complete, turn the oven off but leave the cheesecake inside for an additional 10 minutes.

Remove the cheesecake from the oven and allow to cool, then cut into squares.