Prepare your butternut squash as per my roast butternut squash recipe and start roasting!
20 minutes into your squash roasting time, melt the butter in a large soup pot, and cook the onion, celery, carrot and potatoes for 5 minutes, or until lightly browned.
Add just enough chicken stock to cover your veggies and simmer for about 20 minutes, until your veggies are tender and your squash is finished roasting.
Add the squash to the soup and stir in.
Bring the soup to a boil. Reduce the heat to low, cover the pot, and simmer 10 minutes to let the flavors come together.
Using an immersion blender, blend the soup until smooth. Adjust the consistency with the reserved chicken broth as preferred, then season with salt and pepper to taste.