Preheat oven to 325°F (165°C). Line a 9×13-inch baking pan with parchment paper, leaving an overhang on the long sides for easy lifting. Lightly spray the parchment and sides of the pan with nonstick cooking spray.

Add 30 Oreo cookies to a food processor and pulse until you get fine, sand-like crumbs. Alternatively, place cookies in a zip-top bag and crush with a rolling pin until finely ground.

In a medium bowl, combine the Oreo crumbs, melted unsalted butter, granulated sugar, and a pinch of kosher salt. Stir until evenly moistened and the mixture resembles damp sand. Pour into the prepared pan and press firmly into an even layer, using the bottom of a measuring cup or your fingertips, making sure to press well into the corners.

Bake the crust at 325°F (165°C) for 8–10 minutes, until fragrant and slightly set. Remove from the oven and let cool while you prepare the cheesecake filling.

Using a stand mixer with the paddle attachment or a large bowl with a hand mixer, beat the softened cream cheese on medium speed for 2–3 minutes, until very smooth and creamy. Scrape down the sides and bottom of the bowl to remove any lumps.

Add 1 cup granulated sugar and beat on medium speed for about 1 minute, until combined and slightly fluffy. Beat in the sour cream, vanilla extract, and kosher salt just until smooth. Avoid over-beating at this stage.

Add the eggs one at a time, mixing on low speed just until each egg is incorporated before adding the next. Scrape down the bowl once more and mix briefly on low until the batter is thick, glossy, and smooth.

Gently fold the roughly chopped 12–14 Oreo cookies into the cheesecake batter with a spatula, leaving visible chunks throughout for texture.

Pour the Oreo cheesecake batter over the pre-baked crust and spread into an even layer with a spatula. Sprinkle the top with 6–8 crushed Oreos, if using, for a speckled cookies-and-cream finish.

Bake at 325°F (165°C) for 35–40 minutes. The edges should look set, but the center should still have a slight jiggle when you gently nudge the pan. Turn off the oven, crack the oven door open a few inches, and let the bars sit in the warm oven for 15–20 minutes to cool gradually.

Remove the pan from the oven and let the cheesecake bars cool completely at room temperature, about 1–2 hours. Once fully cooled, refrigerate for at least 3–4 hours, or preferably overnight, until firm.

Use the parchment overhang to lift the chilled Oreo cheesecake slab out of the pan and onto a cutting board. Use a sharp knife, wiping it with a warm, damp cloth between cuts, to slice into 18–24 bars. Serve plain or topped with whipped cream and an optional drizzle of melted chocolate or chocolate sauce.