Place the crushed Oreos in a medium size bowl and drizzle the melted butter evenly over the cookies. Stir to mix completely, then press evenly into the bottom of a 9" springform pan (a regular 8" or 9" pie plate will work just fine as well). Chill in the refrigerator for 30 minutes.
In a medium size bowl with a hand mixer or the bowl of a stand mixer fitted with the whisk attachment, beat the whipping cream until stiff peaks form (about 3-4 minutes; see this tutorial for step-by-step instructions for homemade whipped cream). Place bowl in the refrigerator (or transfer to smaller bowl if using a stand mixer) until ready to use.
In a large bowl with a hand mixer or the same bowl of the stand mixer (no need to clean) now fitted with the paddle attachment, beat the cream cheese on medium-high speed until smooth. Reduce mixer speed to low and add the sugar, increase the mixer speed to medium-high, and beat again until smooth. Add the peanut butter and continue beating. Mixture may become clumpy-- this is ok. Scrape down the sides as necessary.
Turn off the mixer and fold in the cold whipped cream with a large spatula until mixture is smooth.
Pour the filling onto the prepared crust and spread evenly with the spatula (I prefer to use this small offset spatula). Sprinkle with chopped peanut butter cups. Cover with foil or plastic wrap and chill in the refrigerator at least 4 hours (for best results, overnight) before serving. Store leftovers covered tightly in the refrigerator up to 5 days. Pie can be wrapped tightly and frozen up to 2 months. Thaw in refrigerator overnight.