Drain the tuna, chop the anchovies, and set aside.
Meanwhile, put a large frying pan on the fire and warm up the olive oil; once this is warm add to it the onion, garlic, and a bit of salt, mix well, cover the pan and lower the flame to minimum.
Once the onion becomes transparent and soft (on a low flame it should take about 5-7 minutes) add the anchovies, and turn the heat to medium; once the anchovies are lightly fried (1-2 minutes) add the tuna, chili flakes and black pepper and mix well.
Once the tuna changes color, add the tomato paste and parsley to the pan and fry well; then, add the tomato passata, the granulated sugar (if required), and 1 cup of water. Mix well, cover with the lid, and put on low flame again until the tomato sauce is fully cooked. I like to simmer mine very gently for at least 15-20 minutes.
While the sauce is cooking, bring a pan of water to a boil and cook the pasta.
Once the pasta and the sauce are ready, drain the pasta (do not over-drain it!) and add it to the sauce pan with the sauce. Mix it well through and through while on a low flame for about a minute.
The best part of the recipe: serve and enjoy!