To roast garlic: Preheat oven to 400F. Drizzle olive oil over each exposed garlic clove. Cover the bulb with aluminum foil. Bake for 30-35 minutes, or until the cloves feel soft to the touch. Set aside.
In a large soup pot, heat oil over medium heat. Add onions and celery and sauté until lightly golden 5-6 minutes.
Add beans, vegetable stock, salt and pepper. Bring to a boil and reduce heat and simmer for 15 minutes. Remove 1 cup of the bean mixture with a slotted spoon and set aside. Remove skin from roasted garlic and add it to the soup. With an immersion blender, blend soup until smooth. Add reserved bean mixture back to the soup with the fresh thyme and lemon juice, stir to mix. Keep soup warm while preparing the rapini.
In a large sauté pan, heat 2 tbsp of oil over medium heat. Add rapini and sauté for 5 minutes until soft and slightly tender.
Divide soup in bowls and top with rapini and grated parmesan.