Bake a 9 inch pie crust using directions on the box or your usual method for baking a scratch pie crust.
In a 3 quart saucepan, combine the sugar, cornstarch and salt. Gradually add the milk, then add the chocolate chips and egg yolks.
Put the saucepan over medium heat and cook, stirring constantly, until chips melt and mixture is smooth. Continue stirring for another minute or two or until big bubbles break the surface and mixture is about as thick as pudding.
Remove from heat and stir in cream cheese until fully melted. Transfer mixture to a clean bowl and cover with a sheet of plastic wrap. Let cool slightly, then refrigerate until just barely cool. Check every hour.
In a large bowl, beat 1 1/2 cups of whipping cream until soft peaks form. Beat in the vanilla. Reserve 1 heaping cup of the whipped cream for topping, then fold the rest (which should be about 2 cups) into the chocolate mixture.
Sweeten the reserved whipping cream with a little powdered sugar if desired, then spread or pipe over the pie. Chill the pie for at least 5 hours. Garnish top with sprinkles or chocolate shavings.