In a small saucepan, mix together water, dashi powder, light soy sauce, mirin, and sugar over high heat until it comes to a boil. Turn off the heat and transfer to a heat proof dish or glass container. Place in an ice bath until completely cool. If eating later, place in the fridge until the sauce is completely cool.
Cook the soba noodles according to package directions. Immediately drain and rinse with cold water or place in an ice bath to completely stop the cooking process.
When ready to eat, garnish the sauce with sesame seeds and scallions and dip your noodles. You can also serve with grated radish or wasabi. Enjoy!
Notes
Dashi Powder vs. Liquid Dashi: For this recipe, I used dashi powder and mixed with water. If you use liquid dashi, be sure to use the same measurements as the recipe calls for water and omit the dashi powder.Rinse Your Cooked Noodles in COLD Water: It's important to rinse your cooked noodles in cold water immediately, as this will 1. remove any excess starch (which you don't want in your sauce) and 2. stop any residual heat from cooking the noodles further.Optional Garnishes: You can garnish your Cold Soba Noodle (Zaru Soba) with some of these optional garnishes like sesame seeds, chopped scallions, grated radish, or grated fresh wasabi.
Storage
The Tsuyu (dipping sauce) can be stored in an airtight container in the refrigerator for up to one week.Cooked noodles can need in the refrigerator in an airtight container for 2-3 days but I do not recommend this, as the noodles will stick together.