Tosefta for Chullin 214:49

They fulfill [their obligation of eating unleavened bread] with Syrian cakes (which are thicker loaves), whether shaped into figures or whether not shaped into figures. But they may not make Syrian cakes shaped into figures on Passover [itself]. Said Rabbi Yehuda, Boethus ben Zonin asked the the Sages, why is it that they cannot make Syrian cakes shaped into figures on Passover? They said to him, because it takes a woman significant time making them, and [the dough] becomes leavened [during that time]. He said to them, in that case, they can form them using a mold [which would take less time]. They said to him, they will say, all Syrian cakes are forbidden, [but] the Syrian cakes of Boethus are permitted (which would lead to confusion). Rabbi Yosei says, they may Syrian cakes formed into thin wafers, but they may not make Syrian cakes formed into [thick] loaves.