Lightly coat an 8x8-inch square baking pan (at least 2 inches high) with cooking spray. Line the pan with a sheet of parchment paper long enough to extend over two opposite sides by a few inches to form a sling.

Process 22 Oreo cookies in a food processor until fine crumbs form, 30 to 60 seconds. Drizzle in 5 tablespoons melted unsalted butter and pulse until evenly moistened, about 5 (1-second) pulses. (Alternatively, place the cookies in a re-sealable plastic bag and crush with a rolling pin into fine crumbs. Transfer to a medium bowl and stir in the butter.)

Transfer to the baking pan and use the bottom of a flat measuring cup or your hands to firmly press it into an even layer. Freeze for 20 minutes. Meanwhile, make the filling and topping.

Microwave 6 ounces bittersweet chocolate chips and 4 tablespoons room-temperature unsalted butter together in a medium microwave-safe bowl in 30-second increments, stirring between each, until melted, about 2 minutes total. (Alternatively, melt together in a double boiler on the stovetop.) Let cool for 10 minutes.

Beat 2 cups cold heavy cream and 2 tablespoons of the powdered sugar together in a stand mixer with the whisk attachment on medium speed until firm peaks form, 6 to 8 minutes. Transfer to another bowl.

Beat 8 ounces room-temperature cream cheese and ¼ teaspoon kosher salt together in the stand mixer (no need to clean) with the paddle attachment on low speed until smooth, 10 to 20 seconds. Gradually beat in the remaining 1 ⅔ cups powdered sugar until combined, scraping down the sides of the bowl as needed. Beat in 2 teaspoons vanilla extract.

Add the chocolate mixture and stir with a flexible spatula until combined. Fold in half of the whipped cream (about 1 ⅓ cups).

Spread the chocolate filling evenly over the Oreo crust. Dollop the remaining whipped cream on top and spread into an even layer. Garnish with chocolate curls or shavings if desired.

Cover and refrigerate until set, at least 4 hours or up to overnight. Grasping the excess parchment, lift the slab out of the pan and place on a cutting board. Cut into 12 or 16 pieces, wiping the knife clean between each cut for the cleanest-looking slices.