In a medium bowl whisk together 1 cup cold whole milk, 1/2 cup cornstarch, 1 teaspoon kosher salt, 1 teaspoon vanilla bean paste, and 3 egg yolks until smooth; set aside.

In a medium saucepan combine the remaining 3 cups cold whole milk, 3 tablespoons unsalted butter, and 2/3 cup sugar. Heat over medium, whisking frequently, until the mixture is scalding (steam and small bubbles around the edges).

Temper the egg/cornstarch mixture: slowly whisk a small amount of the hot milk mixture into the bowl with the egg mixture to warm it, whisking constantly so the eggs do not scramble. Then whisk the tempered mixture back into the saucepan.

Return the saucepan to medium heat and cook, whisking constantly, until the mixture thickens to a pudding-like consistency. Do not let it boil.

Remove the pudding from the heat and stir occasionally while it cools; it will thicken further as it cools. Wait until the pudding is warm to the touch and not steaming before assembling.

While the pudding cools, make the peanut butter nuggets: in the bowl of an electric mixer combine 1 cup powdered sugar and 1/2 cup creamy peanut butter. Mix on medium speed until small clumps ("nuggets") form. Set the nuggets aside and divide them into three portions: one half and two equal quarters.

Place half of the peanut butter nuggets evenly in the bottom of the 19-inch cooked pie crust. Spoon the cooled pudding over the nuggets and spread into an even layer.

Sprinkle one of the quarter portions of peanut butter nuggets over the pudding. Spread 2 cups whipped cream evenly over the top, then scatter the remaining quarter portion of peanut butter nuggets over the whipped cream.

Refrigerate the assembled pie, loosely covered, for at least 2 hours to set before slicing.