In a medium stockpot, heat milk, ½ cup (115 grams) cream, ¼ cup (50 grams) sugar, and reserved vanilla bean seeds over medium heat just until bubbles form around edges of pot. (Do not boil.)
In a medium bowl, whisk together ½ cup (99 grams) sugar, cornstarch, and salt until combined. Whisk in egg yolks and whole egg until well combined.
Pour about one-fourth of hot milk mixture into sugar mixture, whisking constantly. Pour sugar mixture into remaining hot milk mixture in pot, whisking constantly. Reduce heat to medium-low, and cook, stirring constantly with a silicone spatula, until mixture is thickened and large bubbles begin to break surface in center of pot. Remove from heat, and stir in butter until melted and mixture is smooth. Stir in 1 cup (70 grams) flaked coconut and 1 teaspoon (5 grams) vanilla. Cool custard. Pour half of mixture into cooled blind-baked Pie Dough, and spread into an even layer. Arrange about 10 vanilla wafers on top of filling in a single layer. Top with one sliced banana. Pour remaining filling over the vanilla wafer/banana layer, and repeat. Cover with a piece of plastic wrap, pressing wrap directly onto surface of filling to prevent a skin from forming, and refrigerate.
In the bowl of a stand mixer fitted with the whisk attachment, beat remaining 1½ cups (353 grams) cream, remaining ⅓ cup (66 grams) sugar, and remaining 1 teaspoon (5 grams) vanilla at medium speed until medium peaks form, 2 to 3 minutes. Spread, spoon, or pipe whipped cream on top of pie. Top with remaining ¼ cup (18 grams) flaked coconut and remaining banana slices. Refrigerate until ready to serve.
