Stir the milk and 1/3 cup of the sugar together in a small saucepan. Scrape the vanilla seeds from the bean into the pan and then add the bean. Bring the milk to a boil over medium heat. Remove from the heat, cover the top of the pan with plastic wrap, and let steep at least 1 hour at room temperature, or preferably overnight in the refrigerator.
Strain the milk through a fine-mesh sieve and return to the saucepan. Bring to a simmer over medium heat.
While the milk is reheating, combine the egg yolks and remaining 1/3 cup sugar in the bowl of a stand mixer fitted with a whip attachment. Beat on medium-high speed until the mixture is pale and thick and forms a ribbon when the whip is lifted from the bowl, 3 to 5 minutes.
Switch the mixer to low speed. Slowly pour the hot milk mixture into the bowl and beat just until combined. Do not beat to froth.
Return the mixture to the saucepan and cook over medium heat, stirring constantly, until the custard coats a spoon and registers 160° F on an instant-read thermometer, about 5 minutes. Pour through the fine-mesh sieve into a bowl and stir in cream. Cover bowl and refrigerate the custard overnight.
The next day, churn the custard in an ice-cream maker according to the manufacturer's instructions. Fold the Extra-Bitter Chocolate Sauce into the ice cream by hand.
1 Tahitian vanilla beans are extremely fragrant and have stronger fruit and floral notes than Mexican or Bourbon varieties.
2You can increase or decrease the amount of chocolate sauce in this recipe depending on your preferences. You can also substitute the chocolate sauce for my Burnt Caramel Sauce or add a handful of Burnt Caramel Almonds. Just about any of your favorite inclusions will go well with this versatile vanilla bean base.