Preparation Melt butter in heavy large Dutch oven over medium-high heat. Add corn, yams, celery, zucchini, carrot, onion, thyme and bay leaves. Sauté until vegetables are light brown, about 10 minutes. Add broth and bring to boil. Reduce heat to medium-low; simmer soup until vegetables are very tender, about 45 minutes. Remove bay leaves from soup. Puree 2 1/2 cups soup with vegetables in blender until smooth. Return puree to remaining soup. Add spinach and simmer until wilted, about 10 minutes. Season to taste with salt and pepper.
Preparation Melt butter in heavy large Dutch oven over medium-high heat. Add corn, yams, celery, zucchini, carrot, onion, thyme and bay leaves. Sauté until vegetables are light brown, about 10 minutes. Add broth and bring to boil. Reduce heat to medium-low; simmer soup until vegetables are very tender, about 45 minutes. Remove bay leaves from soup. Puree 2 1/2 cups soup with vegetables in blender until smooth. Return puree to remaining soup. Add spinach and simmer until wilted, about 10 minutes. Season to taste with salt and pepper.