Heat a tablespoon of olive oil in a large pot over medium heat. Add the onion, salt, and pepper and sauté until soft, about 8 minutes. Add the squash and cook until it begins to soften, stirring occasionally, for about 15 minutes.
Add the garlic, sage, rosemary, ginger, and nutmeg. Stir and cook for a 1 minute, then add 4 cups of the broth. Bring to a boil, cover, and reduce heat to a simmer. Cook until the squash is tender, 20 to 30 minutes.
Let the soup cool for about 20 minutes before the next step, otherwise there is a risk of burning. Pour the soup into a blender, working in batches if necessary, and blend until smooth for about 1.5 minutes. If your soup is too thick, add a touch more broth and blend. The blending here is important becuase it is what makes this soup so creamy. Taste for salt and add more if desired.
In a small saute pan, heat the rest of the olive oil. Fry the sage leaves for about 30-45 seconds and set on a paper towel. Top the soup with fried sage, croutons, and a drizzle of olive oil. Enjoy!