Preheat oven to 350°. Lightly spray pie tin with cooking spray.
To make the crust, place chocolate wafers in a resealable plastic bag and, using a rolling pin, smash until fine crumbs form. Transfer to a bowl. Add butter, sugar, and salt and stir to combine. Pour into prepared pie tin. Using base of a glass, flatten crumbs on bottom and sides of pie tin into an even layer. Bake crust for 10 minutes. Let cool completely.
To make the pastry cream, in a bowl, whisk together sugar, salt, and corn starch until no lumps remain. Add ½ cup milk and egg yolks and whisk until smooth.
In a heavy bottomed medium saucepan, combine remaining 1 ½ cups milk, chocolate, and cream. Whisk constantly until near boiling.
Remove from heat and, while whisking briskly, slowly add hot milk to egg mixture. Return to saucepan and continue to cook over medium heat. Constantly whisk until liquid thickens, about 5 minutes. Remove from heat. Add butter and vanilla and stir until mixed well.
Pour pastry cream into cooled crust and spread evenly until smooth. Cover with plastic wrap directly on pastry cream and cool for at least 2 hours. Garnish with chocolate or whipped cream.