Add 400 g dried spaghetti, stir to separate, and cook uncovered, stirring occasionally, until al dente according to package directions (about 8–10 minutes).

Reserve pasta water and drain

Before draining, ladle out and reserve 1 cup of the starchy cooking water. Drain the pasta in a colander and set aside.

Sauce Base

Heat oil and butter

While the pasta cooks, heat 3 tablespoons olive oil and 1 tablespoon butter in a large skillet or sauté pan over medium heat until the butter melts and begins to foam.

Sweat the onion

Add 1 cup finely chopped yellow onion and a pinch of salt. Cook, stirring, until the onion is soft and translucent, about 5–7 minutes—do not let it brown.

Add garlic

Add 4 minced garlic cloves and cook for 30–60 seconds until fragrant, stirring constantly to prevent burning.

Build the tomato sauce

Stir in 1 tablespoon tomato paste and cook 1 minute to caramelize. Add 400 g crushed tomatoes (or passata), 1 teaspoon dried oregano, 1 teaspoon dried basil, 1 teaspoon red pepper flakes, and 1 teaspoon granulated sugar. Bring to a gentle simmer over medium-low heat.

Simmer and season

Simmer the sauce, uncovered, for 10–12 minutes until slightly thickened. Season with 1 teaspoon salt and 1 teaspoon freshly ground black pepper, tasting and adjusting as needed.

Finishing

Combine pasta and sauce

Add the drained spaghetti to the skillet with the simmering sauce. Toss to combine over medium heat.

Loosen with pasta water

If the sauce seems too thick or dry, add reserved pasta cooking water a little at a time (up to 1 cup) until the sauce clings to the pasta and you have a glossy coating.

Add cheese and herbs

Stir in 1 cup grated Parmesan (or Pecorino) and 1 cup torn fresh basil leaves, tossing until the cheese melts and the basil is wilted. Drizzle with 1 tablespoon extra-virgin olive oil and toss once more.

Adjust seasoning and serve

Taste and adjust salt, pepper, or red pepper flakes as desired. Serve immediately, with extra grated cheese and basil on the side.