Trim and thoroughly wash the leek, then cut it in half lengthwise, and slice.
Warm the butter and olive oil in a large frying pan, and add the sliced leek.
Cook over a medium heat, stirring regularly, for 5 minutes, until softened.
Add the minced garlic, and cook for a couple more minutes.
Add the 2 cans of butter beans, along with the vegetable stock, and a few whole sprigs of rosemary.
Cover the pan with a lid, and leave to simmer for around 10 minutes, until the beans are hot and soft.
Add the cream, grated pecorino cheese, and a generous amount of black pepper.
If you used low salt stock, you may also need to salt to taste.
Mix to combine, and simmer gently for a few more minutes, until the cheese has melted and everything is well mixed.
You can add an extra splash of water if you’d like your beans more saucy.
Remove the sprigs of rosemary (don’t worry if a few of the leaves fall off), and serve warm.
