01 - In a medium bowl, combine peanut butter and powdered sugar using a fork. Work the mixture until it forms coarse, crumbly texture. Set aside.
02 - Spread half of the peanut butter crumbs evenly across the bottom of the baked and cooled pie crust.
03 - In a medium saucepan, whisk together granulated sugar, flour, and salt until well combined. Gradually pour in milk while whisking continuously to ensure a smooth mixture without lumps.
04 - Place saucepan over medium heat. Cook the mixture, whisking constantly, until it thickens and just begins to bubble, approximately 4 to 5 minutes.
05 - In a separate heatproof bowl, whisk egg yolks. Slowly drizzle about 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 while whisking constantly. Continue cooking for 2 minutes until the custard becomes thick and glossy.
07 - Remove saucepan from heat. Stir in butter and vanilla extract until fully incorporated and smooth.
08 - Pour the hot custard filling over the peanut butter crumb layer in the pie shell. Allow to cool at room temperature for 15 minutes, then refrigerate for at least 2 hours until completely set.
09 - Using an electric mixer, beat heavy cream, powdered sugar, and vanilla extract on medium-high speed until stiff peaks form.
10 - Spread whipped cream over the chilled pie. Sprinkle remaining peanut butter crumbs on top just before serving.