Heat a large thick-bottomed pot on medium-high heat. Melt the butter in the pot and let it foam up. Add the onion, carrot and celery and saute for 5 minutes. Lower the heat if the vegetables begin to brown.
Add the butternut squash, broth and water. Bring to boil. Reduce to a simmer, cover, and simmer for 30 minutes or so, until the carrots have softened.
Use an immersion blender to pree the soup, or work in batches and puree the soup in a standing blender.
Add pinches of spices. Add salt and pepper to taste. Garnish with chopped fresh parsley or chives.