Preheat your oven to 400°F (200°C). Slice the top off the whole head of garlic, drizzle it generously with olive oil, and wrap it tightly in aluminum foil. Place the wrapped garlic on a baking sheet and roast in the oven for 35-40 minutes, until the cloves are soft and fragrant.

While the garlic roasts, heat 2 tablespoons of olive oil in a large pot over medium heat. Chop one onion and two celery stalks, then add them to the pot. Sauté these vegetables for 5-7 minutes, stirring occasionally, until they soften.

Carefully squeeze the soft cloves into the pot with the sautéed vegetables. Add in 2 tablespoons of chopped fresh rosemary, stirring until the mixture is aromatic, about 1-2 minutes.

Add in two cans of drained cannellini beans, 4 cups of low-sodium vegetable broth, one bay leaf, and season with salt and black pepper to taste. Bring to a gentle boil, then reduce the heat and let the soup simmer uncovered for 20 minutes.

After simmering, carefully remove the bay leaf from the soup. Use an immersion blender to blend the soup to your desired texture.

Turn off the heat, and stir in 2 teaspoons of fresh lemon juice. Adjust seasoning with salt and pepper if needed. Serve warm.