Heat the olive oil in a large nonstick skillet over medium heat. Add the sliced garlic and chili flakes and cook until fragrant, about 1 minute. Lay the dry spaghetti in the pan in a single layer, breaking it to fit. Press down gently and cook undisturbed for about 3 minutes, until the underside is deeply charred. Turn the pasta in sections and toast the other side for another 2 to 3 minutes. Meanwhile, stir the passata, water, and salt together in a jug.

Ladle about 1 cup of the broth into the pan. Scrape up the charred bits with a wooden spatula and stir to separate the spaghetti. Cook, stirring often, until the liquid is nearly absorbed, about 3 minutes.

Continue adding the broth a ladleful at a time, stirring almost constantly, until the pasta is al dente and the sauce is thick and glossy, 12 to 15 minutes. Taste and adjust the salt if needed.

Once the last liquid has nearly evaporated, stop stirring for about 1 minute to let a new charred crust form on the bottom. Slide the spaghetti onto a plate, scrape up every crispy bit, and serve immediately.