Soba Salad with Shrimp, Shiso, and Nori

INGREDIENTS

• 1 small shallot, quartered
• 1 large shell-on shrimp
• 1 kosher salt plus more
• 8 soba (Japanese-style noodles)
• 1/4 mirin (sweet Japanese rice wine)
• 1/4 reduced-sodium soy sauce
• 3 unseasoned rice vinegar
• 1 finely grated peeled ginger
• 1/2 torn fresh shiso or mint leaves
• 3 toasted nori sheets, crumbled (about 1/4 cup), divided