Mr. Rastatter is an employee for a company which produces novel synthetic foods. He was portrayed by Michael McKean.
Mr. Rastatter's company is trying to get "Mockolate", a synthetic chocolate substitute, to the market. He hires Monica to create Thanksgiving-themed Mockolate dishes. However, when the friends try the dishes they are terrible, and Monica gets to use only a tiny proportion of Mockolate to make them edible.
In the end, Mockolate does not get their FDA approval and the project is subsequently shut down.
Monica meets Mr. Rastatter again, this time to be introduced to Fishtachios - pistachios made from reconstituted fish bits. He asks if she's allergic to anything, and when Monica mentions her allergy to cat hair he decides she shouldn't try any.
Mr. Rastatter: Hi, thanks for coming in again.
Monica: Oh, not at all. I have no morals and I need the cash.
Mr. Rastatter: It's like I'm looking in a mirror.