This is the simplest of cool, light summer lunches. I served it with a side of spinach blanched in the water used for the udon and some quickly pan-seared tofu — if weather really won’t permit standing at the stove any longer, though, cold tofu would be delicious too.
I usually think of nori as an optional garnish, but I was surprised by how it added just the right salty touch here — so I think if you can use it, do. If you’re thinning the sauce with a dashi stock that has kombu, though, it’ll add the same sea-breeze savoriness that I liked so much in the nori.
Speaking of dashi, you can make your own (see Nami’s amazing tutorials for awase dashi and kombu dashi) or you can buy dashi powder from a Japanese supermarket. Either one will work — and if all you have is water, that’s just fine too.
Soba buckwheat noodles would be amazing as a gluten-free (or just plain tasty) alternative for dipping, since they’re also delicious cold.
If you don’t have mirin or sake on hand, a bit of seasoned rice vinegar will work as a good substitute, though you may need to adjust for sweetness with a little more sugar.
Finally, if you have a surplus of sesame seeds and don’t feel like buying sesame paste specifically for this, you can easily make your own sesame paste — just toast the seeds briefly until browned and fragrant, then whiz in a food processor, adding a few teaspoons of oil at a time, until it reaches a smooth consistency.