Line an 8x8 inch pan with parchment paper, leaving overhang on two sides, this is your handle for lifting the whole slab out cleanly later.
Pulse Oreos in a food processor until fine crumbs, no chunks. Or crush in a zip-lock bag with a rolling pin if you don't have a processor. Both work.
Mix Oreo crumbs with melted butter until the mixture looks like wet sand and holds together when squeezed.
Press firmly and evenly into the bottom of the lined pan. Use the bottom of a flat glass to compact it, really press it down. A loose crust crumbles when you slice. Freeze for 15 minutes while you make the filling.
Beat room-temperature cream cheese on medium speed until completely smooth, no lumps. This takes about 2 minutes. Don't rush past this step.
Add peanut butter and beat until fully combined and fluffy, about 1 minute.
Add sifted powdered sugar and vanilla. Beat on low first (unless you want a powdered sugar cloud in your face, ask me how I know), then increase to medium until smooth.
In a separate bowl, whip cold heavy cream to soft peaks, not stiff, just billowy. Fold gently into the peanut butter mixture in two additions. Don't stir aggressively, you want to keep the airiness.
Spread filling evenly over the chilled crust. Smooth the top with an offset spatula or the back of a spoon. Refrigerate for 1 hour before adding ganache.
Make the ganache: heat heavy cream in a small saucepan until just simmering, don't boil. Pour over chocolate and butter in a bowl. Let sit 2 minutes, then stir from the center outward until completely smooth and glossy.
Let ganache cool for 5 minutes before pouring, too hot and it melts the filling underneath.
Pour ganache over the chilled filling and tilt the pan gently to spread evenly. Add toppings now if using, flaky salt, crushed Oreos, chopped peanuts.
Refrigerate for a minimum of 4 hours, overnight is better. Every hour past 4 improves the texture.
Lift out using the parchment overhang. Slice with a sharp knife wiped clean between every cut, warm the blade under hot water and dry it for the cleanest edges.