In a large saucepan, heat 2 tablespoons of olive oil over medium heat until shimmering. Add 1 chopped onion and 1 sliced fennel bulb to the pan, stirring frequently. Sauté for about 5-7 minutes until the onion is translucent and the fennel is tender.

Stir in 4 cups of reduced-sodium chicken or vegetable broth, 1 can of drained and rinsed cannellini beans, and 1 can of diced tomatoes. Add 1 teaspoon of dried thyme, a pinch of black pepper, and 1 bay leaf. Bring the mixture to a gentle boil.

Reduce the heat to low, cover the saucepan, and allow your fennel soup to simmer gently for about 30 minutes.

Once the fennel is tender, remove and discard the bay leaf. Stir in 2 cups of fresh spinach and cook for an additional 3-4 minutes until the spinach wilts.

Ladle the soup into bowls and garnish with reserved fennel fronds if desired. Serve hot with crusty bread.