What’s Cooking?

Many years ago, I heard an interesting trivia question asked on a radio show. “Which berachah is recited only on a Wednesday or Thursday?” I was perplexed, though any homemaker who ever had to cook meals for a so-called three-day yom tov should certainly know the answer. I, being just a child then, was stumped. They announced that the answer was the berachah of eiruv tavshilin. At that point in my life, I had only a vague of idea of what eiruv tavshilin is. Customarily, one cooked food item and one baked food item are set aside before yom tov to permit the members of a household to cook on yom tov for Shabbos.
Since an eiruv tavshilin should optimally be made before yom tov, the berachah on eiruv tavshilin is made on a Thursday, when yom tov is Friday and Shabbos. When yom tov falls out on Thursday and Friday, the eiruv tavshilin is made on Wednesday. We will have the opportunity to make three eiruvei tavshilin this Tishrei, before Rosh Hashanah, Sukkos, and Shemini Atzeres/Simchas Torah. I subsequently found out that the trivia question was incorrect. The same berachah that one recites on the eiruv tavshilin, one also recites on eiruvei chatzeiros.