01 - In a medium saucepan, whisk together whole milk, granulated sugar, cornstarch, and salt until well combined.
02 - Place the saucepan over medium heat and cook, stirring constantly with a whisk, until the mixture begins to thicken, about 5 minutes.
03 - In a separate mixing bowl, lightly beat the egg yolks. Gradually whisk in 1/2 cup of the hot milk mixture to gently warm the yolks.
04 - Slowly pour the tempered egg mixture back into the saucepan, whisking continuously. Continue to cook for 2–3 minutes, until the pudding is thick and creamy.
05 - Remove the saucepan from heat and stir in unsalted butter and vanilla extract until smooth. Allow the pudding to cool slightly, covering the surface with plastic wrap to prevent a skin from forming.
06 - In a 2-quart trifle dish or glass bowl, arrange a layer of vanilla wafers, followed by a layer of banana slices and warm pudding. Repeat the layering process, ending with a final layer of pudding on top.
07 - Cover the dish and refrigerate for at least 2 hours, or until thoroughly chilled.
08 - Using an electric mixer, whip the heavy cream, powdered sugar, and vanilla extract in a mixing bowl until soft peaks form.
09 - Spread or pipe the whipped cream evenly over the chilled pudding. Garnish with extra banana slices or crushed vanilla wafers if desired and serve cold.