Whisk together cornstarch, sugar, and salt. Whisk in the egg yolks and milk until fully combined. Add in the chopped chocolate.

Turn on the heat to medium and cook the mixture, whisking constantly, using a spatula, and scraping up any thickened pudding on the edges of the pan.

Cook until the pudding has completely thickened and large bubbles are forming and popping, about 8 minutes. Remove from heat; immediately pour through a mesh strainer into a bowl, using a spatula to push all the pudding out so it's extra smooth.

Whisk in the butter and the extract until combined and fluffy.Pour the pudding into the prepared pie crust and smooth it over the top. Let cool at room temperature before chilling in the refrigerator for at least 3 hours or overnight.

Scoop whipped cream on top of the pie. Using a spatula, spread the cream evenly over the top of the pie. Garnish with additional pieces of chopped chocolate.Keep chilled until ready to serve.