In a small bowl, whisk together cornstarch and fine sea salt. Set aside until ready to use.
In a large sauce pan, warm the milk over medium heat. Do not allow to simmer. Remove from the heat once warmed and set aside.
Combine egg yolks and sugar in the bowl of a stand mixer fitted with a paddle attachment. If you don't have a stand mixer, use a large mixing bowl and a handheld mixer. Beat on medium-high speed until pale yellow and thickened, 3-5 minutes.
Sprinkle in cornstarch mixture and mix until absorbed. Then, mixing on low, stream in the warmed milk. Remove from the stand mixer, and scrape down the sides of the bowl, and whisk to combine thoroughly. Pour the contents of the bowl back into the saucepan.
Transfer to the stovetop and place over medium heat, slowly stirring, occasionally, for about 8-10 minutes or until the mixture reaches a simmer. Reduce the heat to medium-low, and simmer for about 2-3 minutes, until thickened.
Remove from the heat and stir in the butter until melted, followed by the vanilla extract. Refrigerate for 4-5 hours, or until chilled through. The pudding can be made up to 2 days in advance and refrigerated until ready to use.
For the Whipped Cream:
For the whipped cream, combine cream, confectioners sugar, 1 teaspoon vanilla extract and a ¼ teaspoon sea salt in the clean bowl of a stand mixer fitted with the whisk attachment. Alternatively, use a large mixing bowl and a handheld mixer.
Begin beating on low speed until the mixture has just slightly thickened, then crank up the speed to medium-high. Beat for 2-4 minutes, until stiff peaks have formed. Refrigerate until ready to use.
For the Trifle:
To assemble the trifle, in a standard-sized trifle bowl, add a layer of vanilla pudding (about ¾ cup) and spread using an offset spatula or the back of a large spoon. Add a single layer of bananas across the pudding, followed by another layer of pudding. Place Nilla Wafers ™ atop and add one more layer of pudding. Top with 2 cups of the whipped cream. Repeat this exact process once more. NOTE: Both additions will go like this: Pudding, bananas, pudding, wafer cookies, pudding, and lastly, whipped cream.
Place trifle in the refrigerator and allow to chill at least 2 hours before serving.
Notes
You must allow the pudding at least 4-5 hours to completely cool. DO NOT combine warm pudding and cold whipped cream in the same serving vessel. Pudding will be gritty if cooked over too high of a heat setting. Do not be tempted to raise the heat above medium to reach a simmer more quickly.