Heat olive oil in a large pot over medium heat. Add the onion and cook until softened, about 5 minutes, stirring occasionally.

Add the garlic, carrots, and celery, and cook for another 5 minutes, stirring occasionally until vegetables begin to soften.

Stir in the dried thyme, rosemary, and red pepper flakes (if using). Cook for 30 seconds to toast the spices.

Add the rinsed cannellini beans, broth, and bay leaf. Bring to a boil, then reduce heat and simmer for 20-25 minutes until vegetables are tender and flavors have melded.

Remove about 2 cups of soup using a ladle and transfer to a blender. Blend on high for 30 seconds until smooth, then return to the pot and stir well.

If using, stir the fresh spinach into the simmering soup and cook for 2 minutes until just wilted.

Season with salt and black pepper to taste. Remove the bay leaf before serving.

Garnish with fresh parsley and serve hot.