01 - Combine creamy peanut butter and powdered sugar in a medium bowl. Mix with a fork until the mixture reaches a crumbly, sandy consistency. Set aside for later use.
02 - Press half of the prepared peanut butter crumbs evenly into the bottom of the cooled baked pie shell, creating a solid foundation layer.
03 - In a medium saucepan, whisk together granulated sugar, all-purpose flour, and salt until thoroughly blended. Gradually pour in whole milk while whisking continuously to create a smooth, lump-free mixture.
04 - Place saucepan over medium heat. Cook while whisking constantly until the mixture thickens significantly and just begins to bubble. This typically takes 4-5 minutes. Do not allow to boil vigorously.
05 - Whisk egg yolks in a separate heat-proof bowl. Slowly drizzle approximately 1/2 cup of the hot milk mixture into the yolks while whisking vigorously to prevent curdling.
06 - Return the tempered egg mixture to the saucepan, whisking constantly. Continue cooking for 2 minutes until the custard becomes thick, glossy, and coats the back of a spoon.
07 - Remove saucepan from heat immediately. Stir in unsalted butter and vanilla extract until both are completely melted and incorporated into the smooth custard.
08 - Pour the hot custard filling over the peanut butter crumb layer in the pie shell. Let cool at room temperature for 15 minutes, then refrigerate for at least 2 hours or until completely set and firm.
09 - Beat heavy whipping cream with powdered sugar and vanilla extract using an electric mixer until stiff peaks form. The cream should hold its shape when beaters are lifted.
10 - Spread the whipped cream evenly over the completely chilled pie surface. Sprinkle the remaining peanut butter crumbs generously over the top as a garnish. Slice and serve chilled.