Crush Oreos into fine crumbs and mix with melted butter if using
Beat cream cheese until smooth
Add powdered sugar and vanilla and mix well
Whisk pudding mix with cold milk until thick
Fold pudding into cream cheese mixture
Gently fold in whipped topping
Spoon Oreo crumbs into the bottom of serving cups
Add a layer of creamy filling
Repeat layers until cups are filled
Finish with Oreo crumbs on top
Refrigerate before serving