In a medium saucepan, mix together 1 cup sugar, flour, cornstarch, salt, milk, and egg yolks, stirring until smooth. Cook over medium heat until thick and bubbly, stirring constantly. Remove from heat and set aside.
Sprinkle remaining 1 cup sugar in a 10 inch cast iron skillet. Cook over medium heat, stirring constantly until sugar is caramelized – golden color. Remove from heat and carefully pour into warm cream mixture. Stir constantly. It may lump up, but will melt and the mixture will be smooth again. Add vanilla and butter. Stir until smooth. Pour mixture into baked pie shell.
Make meringue out of the egg whites, adding sugar to taste, and spread on top of pie. Bake until light brown. Or forgo the meringue and top with whipped cream.