Melt margerine in large pot over medium heat. Add fennel and leeks. Saute until just translucent, about 15 minutes. Add broth and cover pot. Simmer until vegetables are tender, about 20 minutes. Puree soup in small batches in blender until smooth., adding spinach to last batch before pureeing. Return soup to same pot. Season with salt and pepper. Can be prepared 1 day ahead. Refrigerate until cold, then cover and keep refrigerated. Rewarm soup over low heat, stirring occasionally. Ladle into bowls and serve.
