Mix in a medium saucepan the cornstarch, flour, salt and sugar.
Add boiling water.
Cook and stir over medium heat until the mixture boils.
Lower heat, cover and cook about 10 minutes. (I have had this take as long as 20 minutes).
Add butter, lemon rind, lemon juice and egg yolks.
Cook and stir until thick.
Cool.
Prepare and bake a 9” pie shell.
Cool.
Using 4 egg whites make meringue.
Pile the filling into the cooled shell.
Spoon the meringue on top, spreading well to the edge.
Bake at 300° until delicately brown (15-20 minutes).
MERINGUE:
Put egg whites in a medium sized bowl.
Beat with mixer until soft peaks form when you lift out the beater.
Beat in 1 tsp. at a time the sugar; add salt and lemon juice.
Spoon the meringue evenly over the pie but do not make it too smooth.
Spread well to the edge so that the meringue will not shrink as it bakes.
If a meringue “weeps,” too much sugar was used or the sugar was too coarse.
To cut a meringue pie easily, dip the knife in hot water.
Notes
NOTE: Make sure you completely stir the sugar and cornstarch mixture together well and get all the lumps out before adding the boiling water or the filling will be lumpy.NOTE: Cook the lemon filling over a low heat so it doesn't scorch, and long enough that it will thicken properly.NOTE: The meringue can't be rushed. If you add the sugar too quickly while you are beating the egg whites, the meringue will "weep" after it bakes. That means in will start running, and a gooey clear syrup will appear around the edge of the pie crust.NOTE: Don't add the sugar to the meringue before soft peaks start to form, or the meringue will weep.NOTE: Add about a teaspoon of sugar every 30-45 seconds or so while beating the egg whites. Continue beating while adding sugar and allow it to become thoroughly incorporated before adding the next teaspoonful. It takes time to get through a full half cup of sugar. But even though it may take longer, if you add the sugar slowly, you will end up with a superior meringue.NOTE: Spread the meringue to the edge of the pie or it will shrink back while cooking.NOTE: Cook the meringue in a very slow oven (300 degrees) for about 15-20 minutes or as long as it takes to very lightly brown the top. Don't allow the meringue to scorch on top. Check your oven. Your oven may lightly brown the meringue in 5-10 minutes.NOTE: Pierce the unbaked pie shell with a fork on the bottom and sides before baking so the crust won't shrink while baking.