Look for dried wild mushrooms in the produce section of large supermarkets. Fresh mushrooms shouldn't be substituted; they'll make the soup watery.
Dissolve bouillon cubes in 2 cups boiling water. Set aside.
Bring wine, 1/2 cup chicken broth, and dried mushrooms to a boil in a small saucepan. Remove from heat, and let stand 30 minutes.
Melt butter in a Dutch oven over medium-high heat; add green onions and diced onion. Sauté until tender.
Stir in flour, and cook, stirring constantly, 1 minute. Gradually stir in vegetable broth and remaining 3 1/2 cups chicken broth. Stir in wild mushroom mixture, white mushrooms, and pepper. Bring to a boil, stirring occasionally; reduce heat, and simmer, stirring occasionally, 30 minutes. Cool slightly.
Process mixture, in batches, in a blender or food processor (or use an immersion blender) until smooth, stopping to scrape down sides. Return to Dutch oven.
Cook over low heat, stirring occasionally, 5 minutes or until thoroughly heated. Serve with desired toppings. Garnish, if desired.
Note: For testing purposes only, we used Melissa's dried mushrooms.