Add vegetable broth (or water), bay leaf, butternut squash, pumpkin, celery, and onion to a large soup pot. Place on medium high heat and cook for about 30 minutes (or until the squash is soft). Add sage, salt, and pepper. Simmer for another 3 to 5 minutes.
You can serve this soup as is, or make it smooth by blending it in batches with a blender or using an immersion blender.
Notes
Store leftovers in an airtight container in the refrigerator for up to 3 days.