Heat oven to 450°F. Make pie crust as directed on box for One-Crust Baked Shell using 9-inch glass pie plate. Cool completely.
In heavy 2-quart saucepan, mix 2/3 cup sugar, the cocoa, cornstarch and salt. Stir in milk with whisk until blended. Beat in egg yolks with whisk until blended. Cook over medium heat, stirring constantly, until mixture thickens and boils. Boil and stir 3 minutes. Remove from heat. Add chopped chocolate, liqueur, vodka and vanilla; stir until smooth.
Pour into cooled baked shell. Cover with plastic wrap, placing plastic wrap directly on custard to prevent a tough layer from forming on top. Refrigerate at least 8 hours or until set.
In chilled small bowl, beat whipping cream and 3 tablespoons sugar with electric mixer on high speed just until soft peaks form. Spread whipped cream over pie. Sprinkle with chocolate shavings. Store in refrigerator.