Finely grate the Pecorino Romano cheese and set it aside.

Cut the guanciale into small strips or cubes.

Cut the fresh tuna into bite-size cubes, removing any tough connective tissue.

Bring 6 L water to a rolling boil in the large pot.

Salt the boiling water with 12 g salt and add the 400 g spaghetti.

Cook the spaghetti until very al dente, about 2 minutes less than the package directions.

Cook the 150 g guanciale in the large skillet over medium heat until crisp and its fat has rendered.

Add the 300 g fresh tuna to the skillet and sear it briefly for about 1 minute.

Pour the 350 g tomato passata into the skillet and season with the black pepper.

Simmer the sauce for 5 minutes until slightly reduced.

Reserve 240 ml pasta water, then drain the spaghetti.

Add the drained spaghetti to the tomato, tuna, and guanciale sauce.

Toss the pasta over low heat, adding reserved pasta water a little at a time until glossy and creamy.

Remove the skillet from the heat and toss in the grated Pecorino Romano cheese until emulsified.

Serve immediately with extra black pepper and Pecorino Romano cheese if desired.