Triple Mushroom Soup

• 1 tablespoon butter
• 1/2 cup chopped onion
• 2 cups coarsely chopped fresh shiitake mushrooms
• 1 cup coarsely chopped fresh button mushrooms
• 1 cup coarsely chopped fresh oyster mushrooms
• 1 teaspoon fresh minced ginger
• 3 tablespoons cornstarch
• 3 cups vegetable broth
• 1 cup half-and-half
• 1 1/2 tablespoons vegetable oyster-flavored sauce
• 1 tablespoon coarsely chopped cilantro
• 1 teaspoon coarsely chopped green onion
• 1 teaspoon sesame oil
• 1/8 teaspoon ground white pepper

Garnish:

• Enoki mushrooms, green onion slivers, cilantro leaves