With electric mixer fit with paddle attachment, cream together cream cheese, peanut butter, vanilla extract, and milk for 3 minutes.
Spread peanut butter filling into chocolate cookie pie crust and refrigerate for 1-2 hours to chill.
In medium saucepan, combine butter, chocolate chips, and sweetened condensed milk. Stir at medium heat until smooth. Remove from heat and pour over peanut butter filling layer. Garnish with mini peanut butter cups.
Chill until ready to serve.