On Rosh Hashanah, Jews are supposed to feast. Why? This is said to come from the passage in the book of Nehemiah (8:10): “Go your way, eat the fat, and drink the sweet, and send portions unto him for whom nothing is prepared; for this day is holy unto our Lord.”
The most common custom for Ashkenazi Jews for Rosh Hashanah is the making of sweet challah, primarily round in shape, to symbolize a long life or the unbroken circle of the full New Year to come. Some people place a ladder made of dough on top so our prayers may ascend to heaven, or because on Rosh Hashanah, it is decided “who shall be exalted and who shall be brought low.” Some place a bird made of dough on top, derived from the phrase in Isaiah: “as birds hovering so will the Lord of Hosts protect Jerusalem.”
According to John Cooper in Eat and Be Satisfied, A Social History of Jewish Food, the tradition of baking fresh loaves of bread on a Friday morning among disparate Jewish communities…was a tradition that had its roots in the Talmudic era; strangely enough, this custom was ignored by medieval rabbinic commentators and was revived by the Austrian author of Leket Yosher (a student of 15th-century Rabbi Yisrael Isserlin) and by Rabbi Moses Isserles (the 16th-century Polish scholar of Halacha) at the end of the Middle Ages.