I'm looking for a short story I read a while ago. It might have been part of an anthology. Here is the plot:
The story begins as an owner of a popular new restaurant gets invited to supper by an old man. He goes to the old man's castle and is served a bowl of grey porridge. It smells and tastes wonderful. The old man quickly gulps it down while the butler looks on. It turns out that the butler is several thousand years old. His father was a chef to a French King and created a recipe of the perfect food. If you eat this food and this food only, you will live forever. The father slept with the queen and got his head chopped off, but the son escaped with the recipe. He has been surviving and working for various people throughout the ages and is now currently employed by this old man. The old man is a couple hundred years old and is tired of eating only one food and wants to start eating other foods again, realizing it will kill him. He wants to take care of the butler and help him find a new employer. The new restaurant owner ends up hiring the butler and putting him in charge of a large industrial kitchen with an unlimited budget and lots of employees. They sell little jars of the food and it's really popular because it tastes good, but looks awful.
Anyone recognize it? Remember where it was from?