Before the Meiji era, at which time Japan adopted the Western calendar, the old calendar was based on the phases of the moon. The full moon always fell on the 15th day of the lunar month, and the full moon of the first month of the year was celebrated as Koshogatsu 小正月. Today in Japan, this festival is often celebrated on the 15th day of the 1st month, i.e. January 15th, although this now has no connection to the full moon (what a pity!). Since the Heian era, on the morning of Koshogatsu, a special rice porridge made with red azuki beans and mochi is eaten: In Japanese, this special dish is called azuki-kayu 小豆粥, but in Kyoto it is called azuki-no-okaisan.
At Torin-in, a sub-temple within the Myoshinji temple complex in Kyoto, from the 15th Jan to 31st Jan, you can enjoy visit Torin-in and receive the azuki rice porridge with a beautiful tray of shojin cuisine, as well as an amulet to take home that is for protection from illness and for the prosperity of the family. (Torin-in is the home of Genbo Nishikawa, about whom I have written before. Details about how to participate in this even are given at the bottom of this post.)
At Torin-in there is a special Buddhist ritual performed on the morning of January 15th, which the public are welcome to join, where a little bit of the azuki-kayu is offered to all the trees in the garden of Torin-in, while sutras are being chanted.
Here is the recipe for azuki-no-okaisan from Kyokarashi, a website dedicated to Kyoto obanzai (home-style cooking)
Some azuki beans*
Water as needed
Rice ~ 1/5 cup per person
Round mochi ~ 1 per person
1. Soak the azuki beans overnight and then rinse.
2. Fill a pot with plenty of water and simmer the beans
3. While the mixture is still hot, transfer it to a thermos flask and leave it overnight
4. Make okayu with the rice.
5. Add boiled mochi to the okayu, then add a suitable quantity of the now-softened azuki beans from the thermos.
6. Add salt to taste
With the leftover beans and water remaining in the flask you can make ozenzai by adding sugar, salt, and grilled mochi
*Not giving clear measurements is very typical of Japanese recipes: there is always leeway given for you to experiment and decide how much of an ingredient is to your own taste. Also, where you live affects the ingredients, especially the quality of your water, so the quantity of ingredients will vary according to where it is grown, how old it is, where you live, etc. It is up to you to refine your own sense of taste. However, that’s all well and good if you are an experienced cook! But if you would like a recipe with more concrete details, you can read about how to make red bean okayu (in English) at Just Bento