For crust: Finely crush the Oreos in a food processor. Mix in the melted butter. Press onto the bottom and up the sides of a 9" pie plate. Bake at 375° for 8-10 minutes. Cool completely.
Melt chocolate chips and milk in a glass bowl in the microwave at half power, stirring every 30 seconds till smooth.
Beat the cream till soft peaks form, add the powdered sugar and vanilla. Beat till smooth.
In a large mixing bowl, beat the cream cheese till very smooth. Slowly beat in the melted chocolate mixture. Fold in the whipped cream mixture.
Pour filling into crust and chill for 3-4 hours or till set. Garnish with additional whipped cream if desired.
Notes
You can use milk chocolate or semi-sweet chocolate chips, or a combination of both. I like to use half milk and half dark.
You can substitute an 8-oz container of Cool Whip for the cream, powdered sugar, and vanilla.