How to Make It
Coat an 8-by-8-inch baking dish with nonstick spray. Line the pan with 2 crisscrossed pieces of parchment paper, leaving an overhang on all sides. Coat the parchment with nonstick spray.
Gently split 16 of the Oreos in half. Using a knife, scrape the cream into a large microwave-safe bowl.
Pulse the now-empty Oreos in the bowl of a food processor until fine crumbs form, about 20 pulses.
Add butter to bowl with Oreo cream and microwave on high until butter is melted, about one minute. Stir to combine. Add marshmallows and toss to coat. Microwave, stirring halfway, until marshmallows have melted, about two minutes. Working quickly, fold in Rice Krispies cereal and Oreo cookie crumbs until combined.
Transfer mixture to prepared pan. Coat the bottom of a flat-bottomed measuring cup with nonstick spray and use it to press the mixture evenly into the pan. Crumble remaining two Oreos on top and top with flaky salt, if desired. Let cool completely, about 30 minutes. Cut into 18 squares.