My Amish friend showed me this treat and I couldn’t stop eating it!

1 pre-baked pie crust (9 inches)
1 cup granulated sugar
2 tablespoons all-purpose flour
1/2 teaspoon salt
2 cups whole milk
3 egg yolks, beaten
1/2 cup creamy peanut butter
2 tablespoons unsalted butter
1 teaspoon vanilla extract
1 cup heavy whipping cream
2 tablespoons powdered sugar
Chopped peanuts or chocolate shavings for garnish (optional)