Preheat your oven to 350°F (180°C). Drizzle olive oil over the garlic, wrap in foil, and roast for 60–90 minutes until soft.

In a saucepan, heat olive oil over medium heat. Sauté the diced onion for 5–7 minutes until translucent.

Unwrap roasted garlic and squeeze cloves into the saucepan. Stir in white beans and broth, then add rosemary and boil for 5 minutes.

Blend the soup until smooth using an immersion blender; adjust texture as desired.

Stir in lemon juice and Parmesan if using. Season with salt and pepper, and serve hot garnished with rosemary or chives.