Cut the lemons into quarters 2, bring salted water to a boil. Finely grated rind of 2 lemons and set aside. ;Remove the seeds. Thinly slice crosswise into quarters into triangles. Boil the lemon pieces in boiling water for2 minutes, then transfer to a canvas with a ladle. Dry.
2. Meanwhile, in a large frying pan, heat 1 tablespoon of oil over high heat. Add the pieces of dried lemonand season with a pinch each of salt and sugar. Cook until lemons are caramelized and browned at the edges,3-5 minutes. Transfer to a plate.
3. melt the butter with the remaining oil in the pan over medium heat. Add Chile flakes and zest of twolemons; Cook until fragrant. Whisk in reserved pasta water.
4. squeeze in pasta, 1 lemon juice, cheese, pepper and remaining salt. Cook until the pasta is well coated withthe sauce. Throw the caramelized lemon and celery leaves and parsley if using. Taste and add lemon juice, ifnecessary. Serve, topped with a little olive oil, if you like more cheese and a sprinkle of sea salt.
