Heat the butter and a glug of olive oil in a large saucepan or casserole pot over a medium heat. Add the leeks and fry for 15 minutes until softened and beginning to turn golden brown, stirring occasionally. Stir through the garlic and cook for a further minute.
Add the butter beans into the pan, pour over the hot stock and simmer, uncovered, for 10 minutes.
Meanwhile, fry the chorizo in a small glug of olive oil in a frying pan over a medium heat for 5 minutes, or until oily and crispy, stirring occasionally. Stir in the rosemary and cook for a further minute. Transfer to a serving bowl, along with the oil.
Remove the soup from the heat and blitz it to a smooth consistency with a stick blender. Stir in the crème fraiche and season, to taste.
Ladle the soup into bowls and top with the oily crispy chorizo mixture. Serve with some crusty bread.
Notes
Optional variations:
Spicy version - add chilli flakes or smoked paprika.
Vegetarian version - replace the chorizo with smoked paprika and roasted red peppers, and use vegetable stock.
Extra veg - add carrots, celery or spinach.
Chunky rustic version - don't blend it for a hearty stew-like soup.
This leek, butter bean and crispy chorizo soup is easily adapted if you’re cooking for less or more people.