Melt in a medium saucepan over medium heat:
Finely chop:
Reserve ½ cup of the chopped green onions for garnish. Add the rest to the pan along with:
Cook, stirring occasionally, until the green onions are softened, about 6 minutes. Stir in:
Cook until the mushrooms release their juices, about 4 minutes. Add:
Cook, stirring, for 1 minute. Slowly add while stirring:
Bring to a boil, then reduce to a simmer, cover, and cook for 10 minutes. Transfer half of the soup to a blender and puree until silky smooth. Pour it back into the pan. Remove the pot from the heat and stir in:
Taste and add seasoning if needed. Ladle the soup into warmed bowls. Top each bowl with the reserved chopped green onions.