Preparation Melt 2 ounces bittersweet chocolate with 2 teaspoons vegetable oil and brush over a prebaked 9" pie crust; chill until set. Meanwhile, whisk 3 large egg yolks, 1/2 cup sugar, 3 tablespoons cornstarch, and a pinch of salt in a medium saucepan, off heat, until smooth. Gradually whisk in 2 cups whole milk. Whisking constantly, bring to a full boil over medium heat and boil until thickened, about 1 minute. Remove from heat and whisk in 2 tablespoons unsalted butter and 2 teaspoons vanilla extract. Fold in 3 sliced bananas and let cool slightly. Pour filling into prepared pie crust, cover with plastic wrap, and chill until firm, at least 3 hours and up to 1 day. Beat 1 cup chilled heavy cream with 2 tablespoons sugar and 1/4 teaspoons vanilla extract until firm peaks form; spoon over pie and swirl decoratively.
Preparation Melt 2 ounces bittersweet chocolate with 2 teaspoons vegetable oil and brush over a prebaked 9" pie crust; chill until set. Meanwhile, whisk 3 large egg yolks, 1/2 cup sugar, 3 tablespoons cornstarch, and a pinch of salt in a medium saucepan, off heat, until smooth. Gradually whisk in 2 cups whole milk. Whisking constantly, bring to a full boil over medium heat and boil until thickened, about 1 minute. Remove from heat and whisk in 2 tablespoons unsalted butter and 2 teaspoons vanilla extract. Fold in 3 sliced bananas and let cool slightly. Pour filling into prepared pie crust, cover with plastic wrap, and chill until firm, at least 3 hours and up to 1 day. Beat 1 cup chilled heavy cream with 2 tablespoons sugar and 1/4 teaspoons vanilla extract until firm peaks form; spoon over pie and swirl decoratively.