I have asked in a different question for the citation to the Pri Megadim that I've heard says it's ossur to cook on yom tov for the purpose of eating the food Bein Hashmoshos.
Although a makor for that hasn't been posted yet, I'd like to ask another question in that regard (assuming that the Pri Megadim says in fact what I think he says).
Would it be muter on Shabbos to prepare a food that would be eaten bein hashmoshos, or would this be a problem of "preparing" on Shabbos for the weekday (based on the fact that bein hashmoshos is "sofek lyleh" (possibly night) and is perhaps already the next day, so that it would turn out that the person prepared the food specifically for the next day)? I'm of course speaking of a case where the person's whole intention was to make the food to specifically eat it during the time of bein hashmoshos (if it would be part of the 3rd official Shabbos meal then obviously that would be a different story).