Line an 8x8-inch square pan (at least 2 inches in depth) with parchment paper. Spray the inside of the paper with nonstick spray. Set aside.
Have parchment paper slightly higher than the edges of the pan to make the cheesecake bars easier to lift out once they have cooled.
In a medium bowl, using a hand mixer, beat the slightly melted butter, flour, cocoa powder, and sugar together until smooth.
1 cup unsalted butter, 1 cup all-purpose flour, ¼ cup unsweetened cocoa powder, 3 tablespoons granulated sugar
Use a spatula to spread this evenly in the bottom of the prepared cake pan.
Place in fridge to chill for 30 minutes.
While the crust chills, preheat oven to 350°F.
After 30 minutes, use a fork to poke a few holes into the crust then place in oven to bake for 15 minutes.
Remove crust from oven and allow to cool for 15 minutes before adding in cheesecake batter.
Bake the Cheesecake:
Reduce oven heat to 325°F.
In a large bowl, using a hand mixer, beat the softened cream cheese and sugar together on high speed until smooth.
16 ounces cream cheese, 1 cup granulated sugar
Beat in eggs, one at a time, on high speed until fully combined. Use spatula to scrape down sides of bowl.
2 large eggs
Beat sour cream and vanilla extract into the cheesecake batter until fully combined.
⅓ cup sour cream, 1 teaspoon pure vanilla extract
Place 25 Oreos in an even layer on top of the crust in the cake pan. You’ll have to break a few Oreos in order for them to fit in a single flat layer.
25.03 Oreo cookies
Pour cheesecake batter into the cake pan over top of the Oreo and crust base.
Break the remaining 10 Oreos into small pieces and sprinkle these evenly over top of the cheesecake batter.
9.98 Oreo cookies
Place the cake pan on a baking sheet and bake in oven for 45-50 minutes, or until cheesecake looks set (middle should only have a very slight jiggle).
Chill and Set:
Remove cheesecake from oven and let cool to room temperature for about 1-2 hours.
Once cooled, wrap the cheesecake (still in the cake pan) well in food-safe plastic wrap and place in fridge to chill for at least 8 hours (preferably overnight) before removing from pan and cutting into squares.
Removed chilled cheesecake from pan and cut into 16 squares. Serve cold.
Notes
Becky's Top Tips:
Measure the flour using the spoon-and-level method to prevent a dry crust.
You can use any cocoa powder you prefer, as long as it is unsweetened. Use natural cocoa powder for a more natural taste, and use Dutch-process cocoa powder for a smoother taste.
Use full-fat, brick-style cream cheese -- not the kind in the tub.
Let set for at least 8 hours before slicing.
For clean cuts, run a knife under warm water and wipe between cuts.
Storage: Store Oreo cheesecake bars in an airtight container in the refrigerator for up to 4 days or in the freezer for up to 3 months.