Roast parsnips, carrots, celery root, turnips, sweet potato and butternut squash in large roasting pan with olive oil at 425F until vegies are easily pierced with a fork (30-40 Mins)
Meanwhile, melt butter in large pot over med heat and cook celery and onion until soft.
Pour in vegie broth and bring to simmer uncovered.
Stir in roasted vegies and continue to simmer for 10 mins.
Puree soup and season with salt and pepper.