Place the oreo cookies in a food processor and pulse until fine crumbs form. Transfer the crumbs to a bowl and stir in the melted unsalted butter until the mixture looks like wet sand and all crumbs are moistened. Press the mixture firmly into the bottom and up the sides of an 8-inch pie plate, creating an even layer. Chill the crust in the refrigerator or freezer while you prepare the filling.

In a mixing bowl, whip 1 1/2 cups cold heavy cream using a hand mixer or stand mixer until stiff peaks form. Set the whipped cream aside for use in the filling.

In a separate bowl, beat the room temperature cream cheese and smooth peanut butter together until creamy and well combined. Beat in the powdered sugar and vanilla extract until integrated, resulting in a thick, almost cookie dough-like texture. Gently fold in the whipped heavy cream from Step 2 until the mixture is light and mousse-like. Transfer the peanut butter mousse into the prepared oreo crust from Step 1 and smooth the top. Refrigerate for at least 4 to 6 hours, or overnight, until set. I always like to let the pie chill overnight for an even creamier texture.

Just before serving, whip 1 1/2 cups of cold heavy cream until stiff peaks form. If you like, you can add a few tablespoons of powdered sugar for sweetness, but I actually prefer it unsweetened since the filling is already quite sweet. Use this fresh whipped cream to top the chilled pie just before serving.

Top the pie with the fresh whipped cream from Step 4, then sprinkle with crushed oreo cookies and chopped peanut butter cups if desired. Slice and serve chilled. For extra flavor, I recommend adding the chopped peanut butter cups—their texture and flavor make each bite amazing!