In a medium saucepan or stockpot, bring the chicken broth to a simmer. Stack the spinach leaves on top of each other, and roll them up tightly. Thinly slice into ribbon-like strips. Add the spinach, 6 tablespoons of the sliced green onions, the mushrooms, soy sauce, and white pepper to the broth. When the broth begins to simmer again, gradually add the beaten eggs in a slow and steady stream. Use a fork or a chopstick to create shreds or ribbons with the eggs as they are stirred into the broth-this will shred the eggs into ribbons as they cook. Cook the soup for 1 minute more and remove from the heat. Ladle the soup into bowls and garnish with remaining 2 tablespoons of sliced green onions. Serve hot.