Soba Soup With Shrimp and Greens

If your 1 lb. large peeled, deveined shrimp is frozen, defrost it—here’s how. Meanwhile, soak 1 sheet kombu in 8 cups water in a large Dutch oven until soft and flexible, 15–20 minutes. (You'll probably notice a white layer of film on your kombu—don't rinse that off. It's a source of sweetness.)

While kombu soaks, remove leaves from ½ large bunch or 1 small bunch mustard greens, kale, mature spinach, or Swiss chard (discard or save the stems), wash, and coarsely chop. Thinly slice 10 scallions; set aside about one-third for serving. Peel 1 1" piece ginger. Bring a large pot of salted water to a boil.

Make the dashi: After kombu has soaked, turn heat to medium. Once you see small bubbles around the edges, use tongs to remove kombu. Avoid bringing the water to a boil—it might make your dashi bitter. (As for the kombu, you can save it in the fridge to make another batch of dashi later in the week.)