Preheat your oven to 350°F (180°C). Cut off the top 1/8 inch of the garlic heads and drizzle them with olive oil. Wrap each head tightly in aluminum foil and place it on a baking sheet. Roast for 60 to 90 minutes until the cloves are golden and soft.

While the garlic is roasting, heat 2 tablespoons of olive oil in a large saucepan over medium heat. Add the diced onion and sauté for about 5 to 7 minutes until softened and translucent.

Once the garlic is ready, remove it from the oven and allow to cool slightly. Squeeze the roasted garlic cloves into the saucepan with the onions and cook for 1 minute until fragrant. Pour in the broth, followed by the rinsed white beans and freshly chopped rosemary. Bring to a gentle boil, reduce the heat, and simmer for about 20 minutes.

After simmering, remove from heat. Using an immersion blender, purée the soup until smooth.

Return the blended soup to the saucepan over low heat. Stir in freshly squeezed lemon juice and grated Parmesan cheese if desired. Season with salt and pepper to taste. Serve hot, garnished with optional croutons or fresh herbs.