A popular but somewhat elusive Ashkenazi custom dictates that dairy products be eaten on Shavuot. Midrash Tanchuma (Ki Tissa 9) derives the custom from the idea that milk symbolizes Torah, which is based on the phrase "honey and milk are under your tongue" (Song of Songs 4:11). The land of Israel, in which the rite of presenting the first fruits of the land was performed on Shavuot, is likewise described as "flowing with milk and honey." Indeed, Central European Jews once favored honey cake for dessert on Shavuot, according to Gil Marks' World of Jewish Cooking (p. 314).
Another explanation for the practice derives from Psalm 68:16, which describes Sinai as har gevunim, a "jagged mountain." The word gevunim resembles the Hebrew word for cheese, gevinah. One kabbalistic explanation derives the custom from the gematria (numerical value) of the Hebrew word for milk, chalav, which is equal to forty, the number of days that Moses spent on Sinai. Another derives it from the first letters of the words describing the festival meal offering, minchah chadashah ladonai beshavuoteichem, "an offering of new grain for the Lord on your Shavuot festival," which together spell mi-chalav, "from milk."
Better-known than any of these is the explanation given by the Mishnah Berurah (494:3), which has it that upon returning home after the revelation of the Torah, along with the detailed "oral laws" pertaining to the slaughtering and consumption of meat, the Israelites realized that they could no longer eat the meat they had prepared or use their knives and pots, which were not kosher. Thus, they were forced to eat dairy and parve foods (presumably raw). A variant on this tradition has it that before receiving the Torah, the Israelites thought that dairy products might be considered part of a living animal, which may not be eaten according to the seven Noahide commandments. When they received the Torah and learned that milk was one of the foods with which the land of Israel was associated (e.g. Exodus 13:5), they realized that it could not be forbidden.* They immediately rejoiced with a dairy meal.
Other explanations attribute more pragmatic motives to the Israelites. According to one, the people fasted for three days in preparation for receiving the Torah. When they returned, they were so hungry that they did not have the patience to prepare meat, and resorted to eating dairy instead. According to another, receiving the Torah took so long, that by the time the Israelites returned, their milk had turned to cheese.
Yet another explanation is based on a midrash cited in the Talmud (B. Sotah 12a), which sets the date of Moses' rescue by Pharaoh's daughter at the sixth of Sivan (the date of Shavuot) and states that Moses refused to suckle from Pharaoh's daughter because she was a gentile. For this reason, Moses' mother became his wet nurse. The milk consumed on Shavuot, according to this explanation, reminds us of an important stage in Moses' infancy. An alternative explanation associates the practice with the infancy of corporate Israel, which only truly became a people upon receiving the Torah. Some describe God's granting of the Torah as an act of loving kindness, similar to that of a mother nursing her child. Others focus on the Torah itself as a fundamental source of life, analagous to breast milk. A very different explanation associates meat with a negative aspect of the Sinai experience: the sin of the golden calf. According to this explanation, Jews avoid meat on Shavuot so as not to remind God of their sin.
Perhaps the oddest explanation is based on the Zohar, which compares the seven weeks of sefirat ha-omer (between Passover and Shavuot) to the seven days following a woman's period, during which rabbinic law forbids her contact with her husband. After being separated from God through exile in Egypt, Israel (and her divine counterpart, the shekhinah) had to wait seven "clean" or "white" "weeks of days" before being purified at Sinai through knowledge of the Torah and finally reuniting with God (or, in the shekhinah's case, the aspect of God known as tiferet) in the great cosmic sexual encounter that was the Sinai theophony.** This transition from menstrual impurity to purity is described as a transformation of blood into milk (Be'er Heitev OH 494:3).
Because of the rabbinic dictum that "there is no joy without meat and wine," many observant households (not including mine) make sure to eat a meat meal on Shavuot in addition to a dairy meal. Some commentators cite this practice in their explanations of the custom of eating dairy. Thus, the Remah (OH 494:3) compares the two types of food eaten on Shavuot (meat and dairy) to the two cooked foods eaten on Passover (egg and shank bone), which commemorate the two sacrifices offered on the holiday. A variant on this explanation invokes the two leavened loaves offered on Shavuot. Alternatively, the consumption of both meat and dairy is related to the juxtaposition of the prohibition against cooking a calf in its mother's milk with the commandment to offer the first fruits of the land to God (Exodus 23:19; 34:26), a ritual performed on Shavuot in Temple times. Another explanation relates to the combination of meat and dairy served by Abraham to the three angels in Genesis 18:8. According to Midrash Rabba, the angels were angry at Moses for removing the Torah from heaven and bringing it to earth, but God prevented them from attacking him by reminding them of Abraham's hospitality. Thus, a meal of meat and dairy made it possible for the Torah to be given to Israel.
Isaac Klein, author of A Guide to Jewish Religious Practice, prefers a more rationalist explanation, which he attributes to Hirshovitz, author of Otsar Kol Minhagei Yeshurun ("Collection of all the Customs of Jeshurun"). Klein explains (p. 151): "Meat is the food of those who know no restraint.. . . Eating dairy dishes on Shavu'ot is a reminder that the Torah is given to him who lives the sober life rather than that of pleasure." (Needless to say, the dairy meals eaten in this household on Shavuot are completely out of keeping with Hirshovitz's explanation.)
The presence of so many explanations for a single custom may be a testament to the endless creativity of the Jewish people, but it also draws attention to the fact that no one of these explanations is particularly convincing (although some are highly entertaining). The most probable reason for the practice of eating dairy on Shavuot is that pastoral communities tend to produce most of their cheese in the spring, when sheep, cows, and goats suckle their young. Because of this, springtime festivals the world over tend to feature butter and cheese.
This in no way lessens my enthusiasm for the traditional Shavuot fare of Ashkenazi Jews: blintzes and cheesecake. Although I've never met a cheesecake I didn't like, I have to agree with DH that the very best recipe comes from Joan Nathan's The Jewish Holiday Kitchen.*** Beaten egg whites make this cake delightfully fluffy, without deminishing the richness imparted by the cream cheese and sour cream. Without further ado:
The Very Best Cheesecake
6 tablespoons unsalted butter
1 cup graham cracker crumbs
6 eggs, separated
1 pound cream cheese
1 pound sour cream
1 cup sugar
Juice of 1/2 lemon
1 teaspoon vanilla
2 tablespoons flour
1. Preheat the oven to 300 degrees. Grease the sides of a 9-inch springform pan.
2. Melt the butter and combine with the graham cracker crumbs. Press the crumbs into the bottom of the pan. Save some crumbs.
3. Combine the egg yolks, cream cheese, sour cream, sugar, lemon juice, vanilla, and flour. Beat very well until light and fluffy.
4. Beat the egg whites until stiff peaks form. Fold into cream cheese mixture. Pour the batter into the pan and sprinkle with the remaining graham cracker crumbs.
5. Bake 1 hour. Turn off oven and leave cake in the oven 1 additional hour. Then leave the oven door ajar 30 minutes more.
*This line of reasoning comes from B. Berachot 6b.
**This encounter is repeated each Shavuot at halakhic midnight. You can catch it by staying up for the traditional all-night Torah learning session, or tikkun.
***In fact, it was tasting this cake at my in-law's that convinced me that I had to buy the book.