Preheat the oven to 400°F (200°C). Cut the top off the garlic head, drizzle with olive oil, wrap in foil, and roast for 30 minutes.

In a large pot, sauté the onion, celery, and carrots until softened. Add the roasted garlic, beans, broth, water, rosemary, salt, and pepper. Bring to a boil.

Reduce heat and let simmer for 15 minutes. Blend the soup until smooth, then return to the pot and heat through.