Cook the pasta in plenty of boiling water, following pack instructions until al dente. Drain while reserving some of the pasta water.
A few minutes before the pasta is ready, heat a large pan over low heat. Add the butter and olive oil. Add half of the lemon zest and cook gently for 1–2 minutes.

Transfer the cooked pasta directly into the pan and toss to coat. Add the lemon juice and toss again. Add the grated parmesan cheese gradually, tossing and stirring continuously until emulsified into a smooth sauce.

If the sauce becomes too thick, add some reserved pasta water, 1 - 2 tablespoons at a time, until the consistency is silky. Taste and season with salt and black pepper.

Serve immediately, topping each portion with the remaining lemon zest, chopped basil or parsley, and extra grated parmesan.