Place the whole peeled tomatoes in a large bowl and crush them thoroughly by hand to achieve a rustic, textured consistency.

In a large cold skillet, combine the olive oil, sliced garlic, and red pepper flakes. Place over medium-low heat and cook slowly until the garlic turns golden brown and the oil is fragrant, approximately 4-5 minutes.

Add the crushed tomatoes and their juices to the skillet. Tear half of the basil leaves and stir them into the sauce. Season with kosher salt.

Increase the heat to medium and maintain a steady simmer for 20 minutes, stirring occasionally, until the sauce reduces and the oil begins to separate from the tomatoes.

While the sauce is simmering, bring 4 liters of water to a boil in a large pot. Add 2 tablespoons of salt. Add the spaghetti and cook until 2 minutes before the package's 'al dente' timestamp.

Reserve 240ml (1 cup) of the starchy pasta cooking water, then drain the spaghetti.

Transfer the undercooked pasta directly into the skillet with the tomato sauce. Increase heat to medium-high.

Add 120ml of the reserved pasta water and the unsalted butter. Toss and stir the pasta vigorously for 2 minutes to emulsify the fats with the starches, ensuring the sauce clings to every strand.

Remove the skillet from the heat. Fold in the remaining fresh basil leaves and the grated Parmigiano-Reggiano.

Serve immediately, finished with an optional additional drizzle of extra-virgin olive oil.