In some European communities it was customary to prepare bread in the shape of Mount Sinai, or the tablets of the Ten Commandments.
Some have the custom to bake a challah adorned with a ladder comprised of seven rungs, alluding to the seven heavens G-d rent apart at the time of matan Torah (the giving of the Torah). The numerical equivalent of the Hebrew word sulam (ladder) equals Sinai.
An ancient custom is to bake a long loaf of bread with four heads to commemorate the two bread (shetei halechem) sacrifice offered on Shavuot. Why a long loaf? Because the Torah is referred to as “bread” and it is written that Torah is “longer than the earth’s measure” (Job 11:9). Why four heads? To allude to the verse, “A river flowed out of Eden to water the garden, and from there it separated and became the source of four river-heads” (Genesis 2:10). Torah is compared to a river and Sinai to Eden. Another reason is that the four heads correspond to the four parts of the Torah: peshat, remez, derash, and sod (literal, allusive, hermeneutic, and secret).