In a large pot or dutch oven, combine onion, celery, and oil or butter. Let this saute over medium low heat for 10-30 minutes. The longer it sautes, the sweeter the onions become. I let mine saute the full 30 minutes while I chopped the squash. If you use prechopped squash and want to speed things up, 10 minutes will do just fine.
Add the diced squash and garlic to the pot. Saute for 2-3 minutes. Mix in broth, salt, thyme, black pepper, and nutmeg. Simmer for 30 minutes, or until the squash is tender.
Working in batches, puree the soup in a blender, removing the center from the blender lid and covering it with a cloth to let steam escape. Mix coconut milk into pureed soup.
Serve with garnishes, if desired.
Recipe by Alison's Allspice at https://www.alisonsallspice.com/easy-butternut-squash-soup-with-coconut-milk/