Preheat oven to 400ºF.
Rinse and carefully remove the skin from a 2.5 to 3-lb. butternut squash. Scoop out the pulp and seeds. (Optional: roast the seeds for a soup garnish or snack.)
Cut the squash into chunks and toss with 1 TBSP of olive oil.
Place squash chunks on parchment-lined baking sheet, as spread out as possible. Roast at 400ºF for 25 minutes or until lightly browned.
While the squash is roasting, chop carrots, celery, and onion.
In a large pot, heat 1 TBSP olive oil and 1 TBSP butter (or vegan alternative). Add chopped carrots, celery, and onion. Cook on low to medium heat for about 10 minutes or until tender.
When the squash is done, add it to the pot of vegetables.
Add 4 cups of vegetable broth, cinnamon, nutmeg, and optional salt and pepper to the pot. Let this all simmer for about 10 minutes.
After 10 minutes, let it cool for a few minutes before transferring it with a soup ladle to a blender. Blend on low to medium for about 3 minutes. Use less time if you want a chunkier soup.
Pour the blended soup from the blender into bowls or storage containers. If freezing, let the soup cool before placing a lid on the jar.