In a large saucepan over medium heat, add celery, onion and 1/4 cup of broth. Sauté until onions are translucent.
Add 1/4 cup broth, cauliflower, zucchini and mushrooms and season with salt, pepper, garlic, rosemary and sage. Cook uncovered until tender, about 10-15 minutes.
Add remaining broth (saving 2 Tbsp) and stir to combine.
In a small bowl, mix arrowroot with remaining 2 Tbsp broth to make a slurry. Add slurry to vegetables and simmer uncovered until softened, about 15 minutes.
Finish with salt and white pepper to taste.