Fortunately, a newer copy is in the box, too.
From a box sold in San Antonio, Texas.
1/2 c. sugar
1 T. cornstarch
2 T. lemon juice
2 T. butter
1 c. boiling water
Mix the sugar and cornstarch and the boiling water and a pinch of salt and boil until thick and clear. Continue cooking over hot water for 20 minutes. Beat in the butter, the lemon juice and nutmeg. A grating of lemon rind may be added.