Revised and updated: This recipe for Toshikoshi Soba, or Year-End Soba, traditionally eaten in Japan on New Year's Eve, is one of the earliest recipes posted on Just Hungry. I've expanded the directions so that you can use various methods for making the soup. Originally posted December 30, 2003.
Even though Christmas has become big business in Japan in recent years, the real holiday at this time of year is New Year's Day. The end of the old year, called 師走 (しわす shiwasu), is a hectic time, as people are busily celebrating with friends and colleagues at 忘年会 (ぼうねんかい bounenkai), "forget the year" parties - besides wrapping up things at work and getting ready to go home for the holidays.
New Year's Eve itself (大晦日 おおみそか oh-misoka), however, is celebrated rather quietly by many people. There isn't the big urge to go to a party, to send off the old year with champagne and fireworks and tooting horns. In a way Japanese people do things the opposite of how people in the West celebrate Christmas or Hannukah vs. New Year's Eve and New Year's Day: Christmas is an excuse to have a party (it also happens to be a big 'date' day, when couples stay for the night at a luxury hotel for a romantic party of two). New Year's Eve, New Year's Day and the few days afterwards are when you spend time with family at home. On New Year's Eve, you'll stay home and reflect on the old year, watch some year-ending entertainment programs on TV, and perhaps go to the local temple at midnight, while hearing the 108 rings of the bell to "ring away" the evils of the old year.
The traditional evening meal to have while waiting to greet the new year is a bowl of hot soba noodles, called 年越し蕎麦 (としこしそば toshikoshi soba), which roughly means "end the old year and enter the new year soba noodles". There is no one set recipe for this soba - they are probably as many varieties as there are households. At our house my mother simply prepared a straightforward bowl with hot soup, something on top such as a slice of kamaboko, a rather rubbery fishcake; perhaps some spinach or othe green leavy vegetable, a raw egg dropped on top just before serving. When a raw egg is used like this in a bowl of hot noodles, whether it's soba or udon, it's called 月見 (つきみ tsukimi) - moon-watching.
Hot soba noodles can be enjoyed at any time of the year of course, but since I usually prefer cold soba , New Year's Eve is usually the only day I have this. It is quite good and comforting.
When I originally wrote this article 5 years ago, soba (buckwheat) noodles, were generally only available at Japanese grocery stores. How times have changed! Now you can buy them at many general supermarkets, health food stores and such. There are many different brands, at all price ranges. Look for one that has smooth, mostly unbroken (a few strands may break) noodles that are fairly thick. Avoid the very cheap brands; with soba you really do get what you pay for.
Note that the toppings are not that important here. What is important is properly prepared noodles, and a good flavorful soup. I've given three methods for making the soup, ranging from best (using kaeshi) to ok (using storebought readymade sauce).
Per 1 large bowlful:
Bring a large pot of water to boil. Put in the soba noodles and lower the heat to a simmer. Cook until the noodles are not quite al dente - it should be cooked through. (Dried soba noodles, unlike dried semolina pasta, is rather delicate so you don't want to cook it in a rolling boil.) As soon as it's done, drain the noodles, and plunge it a bowl of cold water. Change the water frequently as you rinse the noodles. The objective is to get rid of any sort of starchy service on the noodles. Once this is done, drain the noodles and set aside in a colander. (See the very detailed instructions on how to cook and rinse soba noodles here .)
If you are using kaeshi , mix 1 part kaeshi to 5 parts dashi stock. Vary to your tastes (don't make it too weak or too strong, but remember that you'll be putting soba noodles in it, so make it just a bit stronger/saltier than you think is necessary).
If you are using soy sauce and mirin straight, first mix the soy sauce and mirin in a 2 to 1 ratio (e.g. 2 Tbs. soy sauce and 1 Ts. mirin). Add a little sugar (for 2 Tbs. soy sauce add 1/2 tsp. or so of sugar). Add dashi to taste, at about the same 1 (soy sauce + mirin + sugar) to 5 (dashi) ratio.
If you are using store-bought tsuyu or mentsuyu (noodle sauce) in a bottle (such as this one ), add plain water to the until it tastes right to you. The ratio depends on the brand and type. Note that even ones that say they are 'straight' (as in, not concetrated) will need to be thinned out for hot noodle soup, since they are meant to be used 'straight' for cold noodle dipping sauce, which is a lot stronger.
Heat up the soup. Put in the rinsed soba noodles, and gently simmer until the noodles are heated through.
Put noodles into serving bowls. Add soup, and any toppings. If you're adding a raw egg (be sure you're only adding a 'safe' egg!), add it at the last moment.
Garnish with a little of the chopped green onion and/or shichimi tohgarashi on top. You could also add a dab of wasabi, a small sheet of nori seaweed, and so on.
七味唐辛子 （しちみとうがらし shichimi tohgarashi or nanami tohgarashi) is a mixed ground spice, containing red pepper, dried citrus skin, sesame seeds, etc. It's a commonly used table spice. You could use ground up red papper flakes as a substitute, though it won't have the same complex flavor and aroma. It's quite inexpensive and lasts a long time, so look for it at a Japanese food store. (Or you can buy it from Amazon Groceries. ) I consider it to be a very important ingredient in my Japanese pantry .
Soup made with dashi, soy sauce and mirin is used for most Japanese noodles. The saltiness or strength of the soup is controlled by the ratio of soy sauce to dashi - the more dashi, the thinner the soup.
See this kitsune udon recipe  for a vegan topping alternative (simmered aburaage or tofu skin). Of course, you could just enjoy the noodles with no topping, just the green onion and shichimi tohgarashi.
Japanese people usually don't do much drinking on New Year's Eve, because it's considered to be a good thing to greet the New Year bright and early. (Drinking during the New Year's festivities is another matter.)