1. Heat the oil in a large pot over medium heat. Add the onion, salt, and several grinds of fresh pepper and sauté until soft, 5-8 minutes. Add the squash and cook until it begins to soften, stirring occasionally, for 8-10 minutes.
2. Add the garlic, sage, rosemary, and ginger. Stir and cook 30 seconds to 1 minute, until fragrant, then add 3 cups of the broth. Bring to a boil, cover, and reduce heat to a simmer. Cook until the squash is tender, 20-30 minutes.
3. Let cool slightly and pour the soup into a blender, working in batches if necessary, and blend until smooth. If your soup is too thick, add up to 1 cup more broth and blend. Season to taste and serve with parsley.