@HDMI1
Non-complicated answer: I checked the raw + dictionary + even the recipe + even bought the butter to check myself. It's Butterfly. I don't known the exact reason why they subbed it as Butterfried or Friedbutter.
Complicate Answer:
Possible Reason 1: The author intended it to be Friedbutter but he wrote it as Butterfly instead.
Possible Reason 2: Funimation made the same mistake as mine. The first part influences the second part which creates a false illusion of fried instead of fly.
Possible Reason 3: They weren't given a script so they translated purely from hearing it. In that case, especially for an English speaker, it can be easily mistaken. It's like "Die" or "Dye", "I" or "Eye".
Unless Author says otherwise, I will stick with Butterfly, faithful to the RAW.