Make the Pastry Cream:

In a saucepan, whisk together sugar and cornstarch, then add milk. Cook over medium heat until it starts to simmer.
In a small bowl, whisk egg yolks, then slowly whisk in a bit of the hot milk mixture. Pour yolk mixture back into the saucepan.
Continue cooking until thickened. Remove from heat, stir in vanilla and butter, then let cool. Spread over the chilled cheesecake layer.
Prepare the Ganache:

Heat heavy cream until it just starts to simmer, then pour over chocolate chips in a bowl. Let sit for 2 minutes, then stir until smooth.
Assemble and Chill:

Pour the ganache over the pastry cream layer and smooth it out.
Chill for at least 1 hour to let everything set.
Serving Suggestion:
Slice and serve with extra ganache drizzle or whipped cream. Enjoy every creamy, chocolatey bite of this Boston Chocolate Cream Pie Cheesecake!