Outside of Israel, we celebrate a Yom Tov for 2 consecutive days. This year, Shavuot comes directly after Shabbat. As I understand it, on such days, one is only allowed to cook in preparation for a 24 hour period (I'm not 100% clear on the limitations of this).
My question is if we can do an Eruv Tavshilin before Shabbat or right before the Yom Tov, so that it becomes permissible to prepare food on the first day for both Yom Tov days. Is Eruv Tavshilin exclusive to Shabbat?