Add 12 oz spaghetti to the boiling water and cook uncovered, stirring occasionally, until al dente according to package instructions (usually 8–10 minutes). Reserve 1 cup of the starchy pasta cooking water, then drain the spaghetti in a colander.

Toss with oil

Return drained spaghetti to the pot or a warm bowl, drizzle 1 tsp olive oil and toss to keep strands separate while you finish the sauce.

Marinara Sauce

Prepare aromatics

Peel and finely dice 1 yellow onion. Peel and mince 4 garlic cloves. Roughly chop 1 cup fresh flat-leaf parsley (reserve 2 tablespoons chopped for garnish).

Sweat onion

In a large skillet or saucepan over medium heat, add 2 tablespoons unsalted butter and 2 tablespoons extra-virgin olive oil. When butter has melted and the fat is shimmering, add the diced onion. Cook, stirring occasionally, until the onion is translucent and soft, about 6–8 minutes—do not let it brown.

Add garlic and parsley

Add the minced garlic and about 1/2 cup of the chopped parsley to the pan. Cook, stirring constantly, for 30–45 seconds until fragrant (do not burn the garlic).

Deglaze with wine

Pour in 120 ml dry white wine and increase heat to medium-high briefly to bring to a simmer. Scrape any browned bits from the pan with a wooden spoon. Let the wine reduce by about half, 2–3 minutes, concentrating the flavor.

Add tomatoes and seasonings

Reduce heat to medium-low. Stir in 800 g canned crushed tomatoes and 2 tablespoons tomato paste until fully combined. Add 1 teaspoon dried oregano, 1 teaspoon red pepper flakes if using, 1 teaspoon sugar (optional), 1.5 teaspoons salt, and 1/2 teaspoon freshly ground black pepper. Bring the sauce to a gentle simmer.

Simmer and meld flavors

Let the marinara simmer gently, partially covered, for 15–20 minutes, stirring occasionally. Taste and adjust salt, pepper, or sugar as needed. If sauce seems too thick, stir in up to 1/2 cup reserved pasta water to reach desired consistency.

Finish with butter and parsley

Off the heat, stir in an additional 1 tablespoon butter (optional for silkiness) and the remaining chopped parsley to brighten the sauce. Stir until butter is melted and incorporated.

Assembly & Serve

Combine pasta and sauce

Add the drained spaghetti to the skillet with the marinara (use a large skillet or return spaghetti to the pot and pour sauce over). Toss gently to coat the pasta evenly, adding reserved pasta water a tablespoon at a time if needed to help the sauce cling to the noodles (use up to 1/2 cup). Warm together over low heat for 1–2 minutes.

Plate and garnish

Divide the sauced spaghetti among 4 plates or bowls. Sprinkle with the remaining 2 tablespoons fresh chopped parsley and grated Parmesan or Pecorino if using. Finish with a grind of black pepper and a small drizzle of extra-virgin olive oil if desired.