Mix melted butter and graham crumbs until combined. Transfer to a springform pan and press into the bottom and sides.
Chill in the refrigerator while you prepare the filling.
Filling
In a large bowl or stand mixer fitted with beaters or a paddle attachment, beat the cream cheese until smooth and creamy. Add the sugar and beat again until fully incorporated and smooth.
In a separate mixing bowl, whisk or beat 1 cup of heavy cream and the vanilla until stiff peaks form. This is important so the filling isn’t too thin.
Gently fold the whipped cream into the cream cheese mixture until mostly combined. Add the crushed Reese’s Pieces and finish folding until just combined. Pour into the prepared crust and spread out evenly with a rubber spatula. Place in refrigerator for at least 4 hours to set.
Ganache
Placed the chopped chocolate in a medium bowl and set aside.
In a small saucepan, heat the heavy cream until slightly simmering. Remove from heat and pour over the chocolate. Wait 3 minutes and then whisk until melted and smooth, then let the ganache sit for 10 minutes to thicken.
Pour the ganache over the cheese cheesecake and top with the uncrushed Reese’s Pieces. return to the refrigerator to chill for at least 1 additional hour.