In a large saucepan, combine the sugar, flour and salt. Stir in coffee until smooth. Cook and stir over medium-high heat until thickened and bubbly. Reduce heat to low; cook and stir 2 minutes longer., Remove from the heat. Stir a small amount of hot filling into egg yolks; return all to the pan, stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer. Remove from the heat. Stir in vanilla. Cool. Fold in whipping cream. Chill. Garnish with additional whipped cream and chocolate if desired.