Put 400g spaghetti or linguine into a large lidded saucepan.
Grate in the zest of 2 large unwaxed lemons and add 1 clove of garlic, olive oil, and flaky sea salt.
Add 1 litre boiling water, cover with a lid, bring to the boil, then simmer for 8 minutes.
Squeeze in the juice of one of the zested lemons and simmer for a final 2 minutes with the lid off.
Take the pan off the heat, stir in salted butter and grated Parmesan, and let sit for a minute or two.
Taste and adjust seasoning if needed, then serve in bowls and finish with Parmesan and torn basil leaves.
