01 - In a medium bowl, combine creamy peanut butter and powdered sugar using a fork until the mixture reaches a crumbly, sand-like consistency. Set aside.
02 - Evenly distribute half of the peanut butter crumble mixture across the bottom of the baked and cooled pie crust, creating a foundation layer.
03 - In a medium saucepan, whisk together granulated sugar, all-purpose flour, and salt until fully combined. Gradually pour in whole milk while whisking continuously to achieve a smooth, lump-free mixture.
04 - Place saucepan over medium heat. Cook while whisking constantly for 4-5 minutes until the mixture thickens substantially and just begins to bubble.
05 - In a separate bowl, whisk egg yolks until smooth. 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 and achieves a glossy sheen.
07 - Remove saucepan from heat. Stir in unsalted butter and vanilla extract until completely melted and incorporated into a silky, smooth custard.
08 - Pour the warm custard filling over the peanut butter crumble layer in the pie shell. Allow to 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. Spread the whipped cream evenly over the chilled pie.
10 - Sprinkle the remaining peanut butter crumble over the whipped cream topping. Slice and serve chilled.