Step 1

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.)

Step 2

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.

Step 3

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.)

Step 4

Add 1 1-oz. package bonito flakes, bring to a boil, and turn off heat. Gently push bonito flakes to submerge, then let stand 2 minutes without stirring. Carefully pour through a fine-mesh sieve into a medium bowl or large measuring cup, being sure to strain out any lingering fish flakes. (You can also save the bonito for your next round of dashi.) That’s it: You’ve made dashi.

Step 5

Wipe out Dutch oven and return to medium heat. Add chopped greens, remaining two-thirds of scallions, and ½ tsp. salt. Using a Microplane, grate in ginger. Pour in ¼ cup water and stir to combine. Cover and cook until greens are wilted, 4–5 minutes.

Step 6

Add dashi, ¼ cup mirin, 5 Tbsp. soy sauce, and 1 Tbsp. toasted sesame oil and bring to a gentle simmer.

Step 7

Carefully lower 4 large eggs into boiling salted water and set a timer for 6½ minutes. Fill up a small bowl with ice water. Immediately plunge eggs into ice bath when your timer goes off. This halts their cooking, keeping them in that gooey yolk state you're looking for. Let cool, then peel.

Step 8

Return salted water to a boil and add 8 oz. soba. Cook 4 minutes, then drain and rinse with cold water. Divide noodles among shallow bowls.

Step 9

Finish up: Pinch tails off shrimp; season with salt. Add to pot and remove from heat. The shrimp will turn bright pink in the residual heat of the broth, a sign that they’re cooked through. Taste and add more salt, if needed.

Step 10

Divide broth among bowls with noodles. Slice eggs in half as you add to bowls. (If you're planning on having leftovers, store the broth, noodles, and uncut eggs separately.) Drizzle yolks with sesame oil and soy sauce. Sprinkle with reserved scallions and 1 Tbsp. toasted sesame seeds.