Begin by melting butter in a large pot over medium heat.
Add the chopped onion, celery, carrot, potatoes, and butternut squash.
Cook for about 5 minutes, stirring occasionally, until the vegetables are lightly browned.
Pour in enough chicken stock to fully cover the vegetables.
Bring the mixture to a boil over medium-high heat, then reduce the heat to low.
Cover the pot and let the soup simmer gently for about 40 minutes, or until all the vegetables are tender, then carefully transfer it to a blender and puree until smooth, working in batches if needed.
Season to taste with salt and pepper.
Serve hot and enjoy your comforting bowl of butternut squash soup.