Mix cream, chicken stock, cider vinegar, egg yolks, flour, sugar, dry mustard, salt and white pepper in double-boiler; whisk constantly over heat until mixture thickens. Cool and then add an equal amount of mayonnaise. Add diced chicken, and onion and celery if desired.
This was really good, but next time I make it I will add a little less vinegar because it was a tad too tangy for me. Would be delicious as a cold meal in the summertime.
