Mix the crushed chocolate-covered pretzels with the melted butter.
Press this mixture firmly into the bottom and up the sides of a 9-inch pie dish. Note: Run a metal measuring cup under hot water to make it easy to press in without it sticking or lifting up.
Chill in the freezer for about 10 minutes to set.
Whip the cream:
In a large bowl, beat the heavy cream until stiff peaks form. Beat in 1/2 cup of the sugar and the vanilla extract. Set aside.Note: If using a stand mixer, scrape whipped cream into another bowl then return the bowl to the mixer stand for the next step; no need to wash it.
Prepare the filling:
In a separate bowl, beat the cream cheese, peanut butter + 1/2 cup powdered sugar until very fluffy, 4 to 5 minutes on high. Pause occasionally to scrape down sides of mixer bowl.
Gently fold in about 1 cup of the whipped cream.
Assemble the pie:
Spoon the peanut butter cheesecake filling into the chilled crust.
Sprinkle the chopped chocolate peanut butter cups evenly over the top.
Spread the remaining 1 cup of whipped cream over the top of the filling and lightly dust the whipped cream layer with cocoa powder.
Chill and serve:
Refrigerate the pie for at least 4 hours, or until firm.
Scoop servings with a spoon or slice the pie with a sharp, warm knife (dip in hot water and wipe dry between cuts).