This is not a pie for anyone who can not stand a little bit a tartness. This pie has a tendency to make people pucker up. For the extra sourpusses at the table the pie can be served with extra lemon sauce! You could use the leftover egg whites to make a meringue but the pie is best without the meringue.
Squeeze the lemons to produce juice. Place the lemon juice in the top portion of a double boiler. Place the bottom portion of the double boiler containing water on your heat source. Allow the water to boil gently. Stir the sugar into the lemon juice. Add a bit more sugar if you do not desire a tart pie. Beat the egg yolks into the lemon juice mixture.
Put the double boiler together and add 5 cups of boiling water to the pan. Cook the mixture for 10 to 15 minutes stirring constantly. In a separate bowl dissolve the cornstarch in a small amount of cold water. Add the cornstarch mixture to the double boiler and keep the mixture boiling until thick. Depending on the size of your lemons you may need to dissolve an additional amount of cornstarch in cold water and add to the mixture to achieve the desired consistency.
Stir the butter into the mixture and remove from the heat source. When the mixture is cool divide the mixture in half and place into 2 cooked pie shells.