Preheat your oven to 350°F. Line a 9×13-inch pan with parchment, leaving an overhang to lift the bars out later.

In a large bowl, combine the chocolate chip cookie mix, softened butter, and 1 large egg. Stir until the dough is sticky and holds together.

Press the cookie dough evenly into the bottom of the prepared pan, forming a compact base. Use the bottom of a measuring cup to smooth it.

Arrange the 24 whole Oreos in a single layer over the cookie base, covering it end-to-end.

In a separate bowl, beat the softened cream cheese with powdered sugar and cornstarch until light and fluffy. Scrape the bowl as needed.

Mix in the sour cream until smooth. Add the two eggs one at a time, mixing until just combined — don’t overbeat.

Fold the roughly chopped Oreos into the cheesecake mixture.

Spread the cheesecake filling gently and evenly over the whole-Oreo layer. Smooth the top with an offset spatula.

Bake in the preheated oven for 35–40 minutes, or until the center is set but still has a slight jiggle. The edges should be slightly puffed and golden.

Cool the pan on a rack to room temperature, then refrigerate for at least 3 hours (overnight is even better).

Lift the bars from the pan using the parchment overhang. Cut into squares with a sharp knife, wiping the knife between cuts for clean edges. Drizzle with caramel if desired and serve chilled.