Prep the pan: Line an 8x8-inch baking pan with parchment paper, leaving overhang for easy lifting. Lightly grease the sides if your parchment doesn’t cover them.

Crush most of the Oreos: Place 28 Oreos in a large zip-top bag and crush with a rolling pin until you have fine crumbs with a few small pieces. You can also use a food processor. Reserve the remaining 8 Oreos for chunky mix-ins on top or in the base.

Make the peanut butter base: In a medium bowl, stir together the melted butter, 1 cup peanut butter, powdered sugar, vanilla, and salt until smooth. Fold in the Oreo crumbs until evenly combined. If using, mix in peanuts or mini chips.

Press into the pan: Transfer the mixture to the prepared pan. Press it down firmly and evenly with a spatula or the bottom of a measuring cup. Aim for a compact, level layer so the bars hold their shape.

Make the chocolate topping: In a microwave-safe bowl, heat the chocolate chips and 2 tablespoons peanut butter in 20–30 second bursts, stirring between each, until smooth and glossy. Alternatively, melt gently on the stovetop using a double boiler.

Top and decorate: Pour the melted chocolate over the peanut butter layer and spread evenly. Roughly chop the remaining 8 Oreos and sprinkle over the top. Press them in lightly so they stick.

Chill to set: Refrigerate for 2–3 hours, or until the chocolate is firm and the base is set. For faster setting, you can chill in the freezer for 45–60 minutes, but don’t leave them frozen for too long or cutting can get tricky.

Slice and serve: Use the parchment overhang to lift the whole slab out of the pan. Warm a sharp knife under hot water, wipe it dry, and slice into bars or squares. Clean the knife between cuts for neat edges.