Q. A lady in Eretz Yisroel that forgot to take off Challah and it’s Leil Sukkos (night of Sukkos) and other bread is not available is there any eitza – (solution to eat the bread)?
A. It is proscribed to eat from bread from which Challah has not been separated. Our Sages prohibited separating Challah on Shabbos or Yom Tov, since one is making something previously unfit for consumption become suitable for use, it is therefore similar to fixing a utensil.
Shulchan Aruch (Y.D. 323: 1) permits after the fact outside of Eretz Yisroel, to eat the bread before Challah is taken, and to leave over a piece and separate Challah from that which is left over after Shabbos. However, that is not permitted in Eretz Yisroel.
Horav Shlomo Miller’s Shlit’a mentioned that there is a possibility of solving similar problems if an Halacha Authority would separate Challah before Shabbos and Yom Tov for all if needed. But it is not known if this is actually done.
You may be restricted to borrow some bread from a neighbor.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a