Gather all the ingredients.
In a large pot, bring water to a boil and start cooking spaghetti according to the package instruction but minus 1 minute because you will cook spaghetti again later.
Konbucha: This is not Kombucha, a fermented drink. Konbucha/Kobucha is made from Konbu seaweed. It is full of konbu glutamine and asparagine umami deliciousness. Konbucha is a salty seasoning so if you can’t find this, you can substitute with kosher salt instead. But Konbu gives nice umami… I hope you can find this seasoning. At Japanese supermarkets, you can find it in the tea section as we drink it as a tea.
Mentsuyu: If you use a store-bought mentsuyu, each brand is different concentrate. Sometimes it's required to dilute 2 x water or 3 x water. Follow the bottle's instruction.
Recipe by Namiko Chen of Just One Cookbook. All images and content on this site are copyright protected. Please do not use my images without my permission. If you’d like to share this recipe on your site, please re-write the recipe in your own words and link to this post as the original source. Thank you.