Prepare the prebaked pie shell; cool completely. In the top of a double boiler set over simmering water, combine 1/2 cup of the hot milk with the sugar and flour. Add 1 1/2 cups of hot milk to the mixture in the double boiler and cook, stirring frequently, for 20 minutes or until thickened. Stir a small amount of the hot custard into the egg yolks. Combine the egg yolk mixture with the mixture in the double boiler. Cook for 2 minutes more. Remove the pan from the heat. Add the vanilla. Beat the peanut butter with the remaining milk. Add the peanut butter mixture to the hot custard. Turn the filling into the pie shell. Preheat the oven to 350 degrees. While the filling is still hot, prepare the meringue. Beat the egg whites, vanilla, and cream of tartar until the mixture holds stiff peaks. Gradually add the sugar, 1 tablespoon at a time, beating until very stiff and glossy. All the sugar must be dissolved. Spread the meringue over the hot filling, sealing it to the edge of the crust. Bake 12 to 15 minutes or until golden brown. Cool, and chill until serving.

One 9-inch single-crust pie