From 1922:

The filling for this pie is made with 2 tablespoonfuls of cornflour dissolved in ½ a cupful of cold water and stirred into 1 cupful of boiling water and cooked for 3 minutes, stirring all the time. Take from the fire, add the juice of 3 oranges and the rind of one, 1 cupful of sugar, pinch of salt; when it becomes cold the yolks of 3 eggs are beaten in. The mixture is then poured into a baked pie crust and covered with the whites of 3 eggs beaten with 4 tablespoonfuls of sugar stiffly. Put in a slow oven and brown lightly.