Date: 3 Kislev 5576
From: Rabbi Moshe Sofer
To: Rabbi Yeshayahu Katz
The responsum discusses the laws of separating challah from dough that contains 'arad' (a type of grain), specifically whether the mixing constitutes a valid 'bilah' (mixture) for challah purposes.
Source: Shu"t Chasam Sofer Collected §18