Add all the ingredients marked with ※ (soy sauce, mirin, sugar, salt) to a small saucepan and heat until it comes to a boil.

Turn off the heat, add the water and dashi powder, and stir well until dissolved.

Pour the broth over chilled udon noodles and top with green onions, tempura flakes, sudachi (or lime), grated ginger, toasted sesame seeds, or grated daikon radish as you like. This broth also works great as a dipping sauce for zaru udon.