Mix your peanut butter with your powdered sugar together until crumbly. Set a side a small amount for top of pie. Sprinkle the rest of the mixture in the bottom of the baked and cooled 9 inch pie crust.
Scald 1 1/2 cups of milk in the top of a double boiler. Make a thickening agent by combining the sugar, cornstarch, flour and salt, then stir in the remaining 1/2 cup of milk with the egg yolks.
Stir this flour mixture into the hot milk and cook it until it thickens.
Remove it from the heat and add the butter and vanilla. Let it cool a little before pouring it over the crumb mixture in the crust. sprinkle the reserved crumbs over the top of the custard and add some whipped cream if desired or you could make a meringue for the top.