01 - In a medium bowl, combine creamy peanut butter and powdered sugar using a fork until the mixture forms coarse, crumbly texture. Set aside.
02 - Evenly distribute half of the peanut butter crumbles across the bottom of the cooled baked pie crust, creating a foundation layer.
03 - In a medium saucepan, whisk together granulated sugar, all-purpose flour, and salt until well combined. Gradually pour in whole milk while whisking continuously to achieve a smooth, lump-free mixture.
04 - Place saucepan over medium heat. Cook the mixture, whisking constantly, until it thickens substantially and begins to bubble, approximately 4 to 5 minutes.
05 - In a separate heatproof bowl, whisk the egg yolks. Slowly drizzle approximately 1/2 cup of the hot milk mixture into the yolks while whisking vigorously to prevent curdling.
06 - Pour the tempered egg mixture back into the saucepan, whisking constantly. Continue cooking for 2 additional minutes until the custard becomes thick, glossy, and coats the back of a spoon.
07 - Remove saucepan from heat. Stir in unsalted butter and vanilla extract until completely melted and smooth. Allow the custard to cool slightly for 5 minutes.
08 - Pour the warm custard filling over the peanut butter crumble layer in the pie shell. Let cool at room temperature for 15 minutes, then refrigerate for a minimum of 2 hours until fully set.
09 - Using an electric mixer, beat heavy whipping cream, powdered sugar, and vanilla extract on medium-high speed until stiff peaks form, approximately 2 to 3 minutes.
10 - Spread whipped cream evenly over the chilled pie. Sprinkle remaining peanut butter crumbles over the top just before serving for optimal texture contrast.