Scald milk. Whisk together sugar, flour, and salt in heavy 6-qt saucepan. Add eggs and egg whites and whisk until smooth. Gradually whisk in milk. Cook over low heat, stirring with wooden spoon, 15 minutes or until custard is thickened and just coats the back of the spoon. Remove from heat and refrigerate. The custard will thicken as it cools. When cold, stir in vanilla, nutmeg, and whiskey.