Heat the butter and a glug of olive oil in a casserole over a medium heat. Add the leeks and fry for 15 mins until softened and beginning to turn golden brown. Stir through the garlic and cook for a further 1 min.

Tip the butter beans into the pan, pour over the hot stock and simmer, uncovered, for 10 mins. Blitz to a smooth consistency with a hand-held blender, then stir in the crème fraîche and season to taste. Keep warm over a low heat.

Meanwhile, fry the chorizo in a small glug of olive oil in a frying pan over a medium heat for 5 mins or until oily and crispy. Stir in the rosemary, cooking for a further minute. Ladle the soup into bowls and top with the rosemary and chorizo mixture, as well as any oil left in the pan. Serve with some crusty bread.