From: Rabbi Moshe Sofer
To: Rabbi Leib
If a Shabbos challah broke into many pieces, may one pin them together with wooden splints to fulfill lechem mishneh? The Chasam Sofer rules that while reattaching a single broken piece is permitted by some authorities, reassembling many fragments extends the leniency beyond its established scope, especially since the Rambam rejects the underlying principle entirely. One should obtain another complete loaf instead.
Source: Shu"t Chasam Sofer OC §46