Heat the oven to 400 F. In a roasting pan, toss squash with 1 teaspoon of oil. Roast for 40 minutes or until brown. Set aside.
In a large pot, add the remaining oil, celery, onion, spinach, garlic and carrot. Saute over medium heat until vegetables are lightly browned. Add stock, sage, nutmeg, pepper and roasted squash to the pot, and simmer for a few minutes.
Carefully puree soup with a stick blender, or process soup in batches in a blender or food processor. Return pureed soup to pot and bring back to a simmer. Serve.