In a large heavy saucepan, combine the sugar, flour and salt. Gradually whisk in milk and eggs until smooth. Cook and stir over low heat until a thermometer reads 160°, about 20 minutes. Remove from the heat; stir in extracts. Cover and refrigerate until well chilled, about 2 hours.
Just before serving, strain eggnog mixture; stir in the cream and nutmeg. Pour into glasses. Yield: 18 servings (about 3 quarts).