To prepare the shrimp filling: With a knife, chop the shrimp into small pieces. Transfer the shrimp to a mixing bowl. Add the cornstarch, salt, white pepper, and sesame oil. Mix until well combined.
To assemble the siu mai: Place a wonton wrapper in the palm of your hand. Using a dining knife or butter knife, scoop about 1½ tablespoons of the shrimp filling into the center of the wrapper. Place the wrapper between your thumb and index finger. Use the knife to gently press the filling down while turning the siu mai to wrap it firmly into its classic open-top shape. Top each siu mai with one small shrimp and a few pieces of minced carrots. Repeat with the remaining filling.
To steam the siu mai: Lightly brush the bamboo steamer with the cooking oil to help prevent sticking. Arrange the siu mai in the steamer, leaving a little space between each one. Bring water to a boil in a large steamer over high heat. Place the bamboo steamer inside, cover, and steam for about 5 minutes, or until the shrimp is completely cooked through. Carefully remove and serve.
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Notes
Hand-chop the shrimp: Chopping the shrimp by hand creates a juicier, springier texture than processing it into a paste.Food processor shortcut: If you're short on time, pulse the shrimp a few times in a food processor, but leave some texture for the best bite.Don't worry about perfect shaping: Gently press and shape each siu mai in your hand. They don't have to look identical to steam beautifully.Brush the steamer: Lightly brushing the bamboo steamer with cooking oil helps prevent the siu mai from sticking.Prep ahead: Mix the shrimp filling up to 24 hours ahead or assemble the siu mai up to 12 hours before steaming. Keep them covered in the refrigerator.Freeze for later: Freeze the assembled, uncooked siu mai in a single layer. Once frozen, transfer them to a freezer bag and steam directly from frozen for 7–8 minutes.