Make the crust: Add Oreo cookies to food processor. Process cookies to fine crumb (alternatively, you can place the cookies in a resealable plastic bag and bang/roll with a rolling pin to a fine crumb). Transfer cookies to a medium bowl. Add butter. Stir mixture with fork until well combined.

Press crumb mixture evenly into bottom and sides of 9-inch pie plate. Refrigerate at least 30 minutes.

Meanwhile, in small saucepan over medium heat, whisk sugar and eggs until mixture reads 160 degrees F with an instant-read thermometer. Remove from heat; stir in baking chocolate until smooth. Cool slightly, about 5 minutes, then stir in butter until melted. Cool mixture until just warm, stirring occasionally.

In large bowl, beat heavy cream with electric hand mixer until soft peaks form. Add powdered sugar; beat mixture until stiff peaks form.

Carefully fold half of whipped cream into cooled chocolate mixture. Pour filling into chilled pie crust. Cover and refrigerate at least 2 hours to set. Cover bowl with remaining whipped cream and refrigerate until ready to serve.

When ready to serve, spoon and spread whipped cream in a heap on top of chilled pie. Garnish with grated extra baking chocolate and crumbled Oreo cookies. Store leftovers covered in refrigerator.