Cook the rice. Start your rice first so it’s ready when the shrimp are done. Keep it warm and fluffy.
Prep the shrimp. Pat dry and make 2–3 shallow cuts on the underside to keep them from curling too tightly.
Lightly season with a pinch of salt.
Heat the oil. In a deep pot or skillet, pour 1.5–2 inches of oil. Heat to 350–360°F (175–182°C). Keep a thermometer handy for consistent results.
Make the sauce. In a small saucepan, combine soy sauce, mirin, sugar, and dashi (plus ginger if using).
Simmer 2–3 minutes until the sugar dissolves. Keep warm.
Whisk the batter. In a bowl set over an ice bath, lightly beat the cold egg with the cold water. Sift in flour, cornstarch, and a pinch of salt.
Stir gently with chopsticks or a fork just until combined. Leave small lumps; overmixing makes it heavy.
Dust the shrimp. Toss shrimp in a little flour to help the batter cling. Tap off excess.
Fry the shrimp. Dip each shrimp in batter and slide it into the hot oil. Fry in batches 1.5–2 minutes, turning once, until pale golden and crisp.
Avoid overcrowding. Transfer to a rack or paper towels and salt immediately.
Optional veggie tempura. Dip quick-cooking veggies (thin slices work best) in batter and fry 1–2 minutes until crisp. Drain and lightly salt.
Assemble the bowls. Spoon warm rice into bowls.
Add shrimp tempura and any veggie tempura. Drizzle with the warm sauce (or serve on the side to keep things ultra-crisp).
Finish and serve. Top with scallions, sesame seeds, and nori. Serve right away for the best crunch.