Banana Marshmallow Cream Pie

Prepare the prebaked pie shell, cool completely. Preheat the oven to 425 degrees. Melt the butter in the top of a double boiler set over simmering water. Stir in the flour and cornstarch. Slowly stir in the hot milk, then add the sugar. 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. Add the 12 quartered marshmallows to the hot custard in the double boiler. Cook for 2 minutes more. Remove the pan from the