Trim the root and any dry ends from the fennel. Thinly slice the bulb. Peel the onion and thinly slice it. Peel the garlic cloves and crush or finely chop. Pick the rosemary leaves off their woody stalks and finely chop them.
Pour 1 tbsp oil into a pan and warm to a medium heat. Slide in the chopped onion, fennel and rosemary. Sprinkle in a pinch of salt and pepper. Cook for 10 mins, stirring every so often, till the veg are soft and lightly caramelised. Stir in the chopped garlic and continue to cook for 1 min.
Drain and rinse the cannellini beans, and tip them into the pan. Crumble in the stock cube. Pour over 750ml boiling water and give the pan a stir. Bring the soup to the boil, then reduce to a simmer and cook for 10 mins.
When the soup is cooked, grate in the blood orange zest. Squeeze in half of the juice. Have a taste of the soup and add more salt and pepper if needed. Ladle into bowls and serve with wedges of the remaining orange half for squeezing.