Prepare the shrimp and vegetables. Pat the peeled shrimp dry and roughly chop it into small pieces. Finely dice the bamboo shoots, scallions, and garlic, and grate the ginger. Thaw frozen peas if using. Keeping the vegetables finely chopped helps the dumplings hold together.
Mix the filling. In a bowl, combine the ground pork, shrimp, bamboo shoots, scallions, garlic, ginger, soy sauce, sesame oil, potato starch, pepper, and salt. Stir for 1–2 minutes until the mixture feels slightly sticky and holds together. Refrigerate while you prepare the steamer. Do not taste the raw filling; season by the measured amounts and adjust in a future batch if desired.
Prepare the steamer. Bring water to a steady boil in a pot fitted with a steamer basket. Line the basket with perforated parchment or a cabbage leaf, leaving the steam openings clear. Keep the water level below the basket. A steamer liner prevents sticking; leave space between dumplings for circulating steam.
Shape the shumai. Set a wonton wrapper in your hand and place about 1 heaping tablespoon of filling in the middle. Bring the edges up around it, gently gathering them to form an open-topped cup. Press the base flat and place one pea on the exposed filling. Repeat until you have 16 dumplings. If using square wrappers, fold or trim the corners neatly; the top should remain open.
Steam in batches. Arrange the dumplings upright in the steamer without overcrowding. Cover and steam over steadily boiling water for approximately 12–15 minutes per batch, or until the center of the pork filling reaches at least 160°F (71°C) and the shrimp is opaque. Repeat with the remaining dumplings as needed. Two batches may take roughly 30 minutes of steaming; adjust for steamer capacity and confirm doneness with a clean food thermometer.
Make the dipping sauce and serve. Combine the Chinese black vinegar and soy sauce in a small dish, if using. Transfer the cooked shumai to a plate and serve warm with the sauce. Use clean utensils and avoid contact between cooked dumplings and raw filling.
