Preheat oven to 450 degrees.

In a medium heavy saucepan over low heat, whisk together 1 cup of heavy whipping cream, chocolate, granulated sugar, and butter. Continue to stir and whisk for about 10 minutes or until chocolate completely melts then remove pan from heat. 

Next, quickly whisk ⅓ of hot mixture into the egg yolks making sure the yolks don’t scramble. Return egg yolk mixture to saucepan whisking quickly. Continue cooking over medium-low heat for about 5 minutes or until everything slightly thickens and begins to bubble then remove from heat. (Mixture might appear slightly curdled.) 

Stir in remaining 3 tablespoons of whipping cream and peppermint extract.

Place saucepan in a bowl of ice water and let stand about 20 minutes or until mixture stiffens and becomes difficult to stir, stirring occasionally.

Transfer chocolate mixture to a large Pyrex mixing bowl. Beat with an electric mixer on medium to high speed for 2 to 3 minutes or until light and fluffy. Spread chocolate mixture into pastry shell. Cover and chill for 5 to 24 hours. Top with whipped cream and peppermint and serve.