Step 1

Combine mirin, sugar, and soy sauce in a small saucepan and set over medium heat. Cook, stirring, until sugar is dissolved. Transfer to a bowl and set in the refrigerator to chill. (You can also rapidly cool by pouring mixture into a stainless steel mixing bowl and nesting that bowl in a slightly larger mixing bowl filled with ice water.)

Step 2

Combine 1/4 cup of the soy/mirin mixture (kaeshi) with dashi and stir. Taste mixture and add remaining kaeshi if desired. Keep chilled.

Step 3

In a medium pot of boiling water, cook udon until just tender, 2 to 3 minutes (or follow cooking time on package if it differs). Transfer to an ice bath to chill. Drain noodles well.

Step 4

Transfer noodles to 2 soup bowls. Top with garnishes and condiments of your choice, then pour dashi broth into each bowl and serve.