To make the Vegan Tsuyu Sauce, add water, kelp and shiitake mushroom into a pot and let it soak for at least 15 minutes.
Add soy sauce and mirin and bring to a boil. Right before it comes to a full boil, remove the kelp.
Once boiling, turn the heat to low and simmer for 10 minutes.
Remove the shiitake mushrooms and pour the broth into a heat-safe jar or container and place into the fridge to cool down. Store this sauce in the fridge for up to 2 weeks to enjoy later - this broth recipe should make around 4-6 servings.
Boil soba noodles, according to instructions, then rinse them thoroughly in cold running water. Drain.
Prepare desired condiments such as grated daikon radish, shredded nori, and/or julienned cucumber.
Place cold soba noodles onto a plate and top with nori (optional), cucumber (optional), and sesame seeds (optional).
Pour around 1/4 - 1/3 cup of prepared dipping sauce into a small bowl per serving (add 2-3 ice cubes if not fully cold). Add green onions, wasabi (optional) and grated radish (optional) and mix with chopsticks.
To eat, pick up a bite-sized amount of noodles then dip into the sauce, swirl around and enjoy!