Melt the butter in a frying pan. Add the sage leaves, then cook on a low heat until the butter turns nutty and smells biscuity. Scoop out the sage leaves and set aside. Add the stock and half the lemon juice, and whisk well.

Bring a large pan of salted water to the boil. Tip in the pasta and cook following pack instructions, then use tongs or a spaghetti spoon to transfer it to the butter pan. Toss well, adding a spoonful of the pasta water if needed to loosen the sauce. Add extra lemon juice and seasoning to taste.

Divide between warm pasta bowls and serve topped with the sage leaves, lots of black pepper and parmesan.