I think this is a pretty perfect example of how you can achieve something that tastes authentically Japanese with minimal effort and with minimal ingredients. As long as you can buy some Udon noodles and clams, you’re all set! While it’s often difficult to have access to good quality noodles like Soba or Ramen, I find that Udon is the easiest to find of decent quality. Even frozen Udon has come a long way as they are flash frozen after blanching, so they are al dente. (*I wouldn’t recommend dry Udon though, unless you buy Inaniwa Udon to eat cold)
The clams photographed below were cherry stone clams that I got from P.E. & D.D. at the Union Square Farmers Market (NY) and I only had to use about half a dozen for a portion of soup. I actually don’t particularly like using these New England clams for soup because I don’t think the broth they give is as nice as clams in Japan (which are more similar to Manila clams), but it’s best to use what’s fresh and available locally!
You can use Kombu (dried kelp) if you want more Umami in your soup, but if you don’t have any, that’s fine. Bring about 300-400ml of water to a simmer and add the clams (you’ll want to have cleaned them by keeping them in some salted water for a while until they purge out all the sand- if you don’t have time just wash them well under the tap!). As each shell opens, remove them and keep them in a bowl. Season the soup with some soy sauce (I used a white soy sauce to keep the colour light). Boil the noodles in a separate pot and drain well before combining with the hot broth. Garnish with the clams and some scallion. I would say that this is closer to being a Kansai-style Udon (more Kombu-based and seasoned with light soy sauce, while Kanto-style is darker in colour because the soup is made with Katsuobushi and regular soy sauce).