Prep the pan: Line an 8x8-inch baking pan with parchment, leaving overhangs for easy lifting.
Lightly grease the parchment.
Crush the Oreos: Add cookies to a food processor and pulse to fine crumbs with some small bits for texture. No processor? Seal cookies in a zip-top bag and crush with a rolling pin.
Mix the base: In a large bowl, combine Oreo crumbs, melted butter, 1 cup peanut butter, powdered sugar, vanilla, and a pinch of salt.
Stir until evenly combined and thick like a stiff dough.
Press into the pan: Transfer mixture to the prepared pan. Use a spatula or the bottom of a measuring cup to press it firmly and evenly into the corners.
Melt the chocolate: In a microwave-safe bowl, heat chocolate chips with 2 tablespoons peanut butter in 20–30 second bursts, stirring after each, until smooth and glossy. Don’t overheat.
Add the topping: Pour the warm chocolate mixture over the Oreo-peanut butter layer.
Spread into an even layer. Tap the pan gently to smooth out air bubbles.
Finish with extras: While the chocolate is still soft, sprinkle crushed Oreos, chopped peanuts, or flaky salt on top. For a swirl, drizzle warmed peanut butter in thin lines and drag a toothpick through.
Chill to set: Refrigerate for 1–2 hours, or until the chocolate is firm and the base is set.
Slice and serve: Lift the slab out using the parchment.
Warm a sharp knife under hot water, dry it, and slice into bars. Wipe the knife between cuts for clean edges.