1. Fill a medium pot with water and bring to a boil over high heat. Add salt and return to a boil. Add edamame and cook until tender, about 10 minutes.

2. Drain edamame and transfer to the bowl of a food processor along with heavy cream, butter, remaining 1 teaspoon salt, and truffle oil, if using. Process until smooth.

3. Place 1 teaspoon edamame mixture in each dumpling wrapper and fold to enclose. Place dumplings on a parchment-lined baking sheet and cover with a moist paper towel; set aside.

4. Fill a large saucepan or wok with 2 cups water; bring to a boil. Set a bamboo steamer over saucepan and add dumplings. Cover and steam until tender, about 5 minutes. Serve immediately in warmed chicken broth and garnish with onion sprouts, if desired.