Cut off the white pith covering the lemon and discard.
Cut the lemon into segments and pry off the seeds.
Boil of cup of water and blanch the lemon segments for a minute. Scoop out and drain on paper towels.
Heat the butter and olive oil. Add the blanched lemon segments with the sugar, lemon zest and chili. Cook over medium heat, stirring often, until the mixture thickens and turns a shade darker. Don't worry if the lemon segments almost liquefy.
Add the anchovy fillets, breaking them into bits as you stir.
Throw in the cooked pasta. Season with a little pepper. Toss to coat the noodles with sauce.
Add the Parmesan and parsley. Toss a couple of times more. Taste and add salt, if needed.
Twirl the pasta into a shallow bowl. Top with more anchovy fillets, chopped parsley and grated Parmesan.