Preheat your oven to 350°F (180°C), prepare the garlic heads by cutting the tops off, drizzling with olive oil, and wrapping them securely in aluminum foil. Place the wrapped garlic in the oven and roast for 60-90 minutes until golden brown and soft.

In a large saucepan, heat a tablespoon of olive oil over medium heat. Add the diced onion and sauté for 5-7 minutes until translucent.

Squeeze the roasted garlic from its skins into the pan with the onions, sautéing everything for an additional minute.

Pour in the broth, adding the white beans and fresh rosemary. Bring to a boil, then reduce the heat and let it simmer for about 5 minutes.

Using an immersion blender, carefully purée the soup directly in the pot until smooth. Alternatively, transfer to a traditional blender in batches.

Stir in the grated Parmesan cheese and freshly squeezed lemon juice. Season with salt and pepper to taste.

Ladle into bowls, garnish with additional Parmesan, herbs, or croutons, and serve hot.