Bring 4 cups (960 ml) (1 liter) of water to a boil in a medium saucepan.
Add the baby bok choy and blanch for exactly 1 minute.
Drain immediately and rinse under cold water to stop the cooking process.
Slice the blanched baby bok choy in half lengthwise. Gently pat them dry with a clean kitchen towel or paper towel.
Cut the sheet of nori crosswise into 12 thin, even strips.
Dip your fingertips in water to prevent sticking. Scoop about 2 tablespoons (30 ml / 1 fl oz) of prepared sushi rice and gently squeeze and shape it in your palm to form a neat rectangular bed.
Repeat to create 12 rice beds.
Lay one baby bok choy half, cut side down, on top of each rice bed.
Secure the bok choy by wrapping one nori strip around the center of each piece, like a little seatbelt. The moisture from the rice will help seal it.
To serve, arrange the nigiri on a platter. Carefully spoon ½ teaspoon of the Black Bean Sauce over each piece and finish with a generous sprinkle of fresh orange zest.
Keep a small bowl of water mixed with a splash of rice vinegar (called tezu) nearby.
Dipping your fingers in it prevents the sticky sushi rice from clinging to your hands as you shape the nigiri.
Don't over-blanch the bok choy. A quick 1-minute dip followed by an ice bath keeps it tender-crisp and preserves its vibrant green color.
