Melt butter in a large pot over medium heat, and cook onion, celery, carrot, potatoes, and squash until lightly browned, about 5 minutes. Pour in enough chicken stock to cover vegetables.
Bring to a boil over medium-high heat. Reduce heat to low, cover pot, and simmer until all vegetables are tender, about 40 minutes.
Transfer soup to a blender and process until smooth. Return to the pot and mix in any remaining stock to reach desired consistency. Season with salt and pepper.
Serve hot and enjoy!
