Start with cold oil and garlic. Add the olive oil and smashed garlic cloves to a cold wide pan or Dutch oven. Turn the heat to medium-low. Allow the garlic to slowly warm in the oil, turning occasionally, until it is fragrant and just beginning to turn golden at the edges — about 5 to 6 minutes. This gentle infusion flavors the oil without burning the garlic. Remove the garlic if you want a cleaner sauce, or leave it in to break down. If using onion, add the halved onion now and cook until softened, about 8 minutes, then remove.

Add the tomatoes. Crush the San Marzanos by hand directly into the pan — squeeze each one until it collapses, add all the juices from the can. The pan will spit and hiss. Stir to combine with the garlic oil. Add the salt.

Simmer uncovered. Raise the heat to medium and bring to an active simmer. Cook uncovered, stirring occasionally, for 20 to 25 minutes until the sauce has reduced by roughly a third and the color has deepened from bright red to a darker, more concentrated crimson. The surface should be bubbling steadily throughout — not violently boiling, not barely simmering. Taste and adjust salt. If the tomatoes were particularly acidic, add a pinch of sugar.

Finish with basil and oil. Remove from heat. Tear the basil leaves directly into the sauce. Drizzle with a generous pour of good olive oil — do not stir this in completely, let it pool slightly on the surface. The raw olive oil finish is not optional. It adds brightness and a grassy richness that cooked olive oil cannot provide.

Toss with pasta. Cook your pasta until 1 minute before al dente in well-salted water. Reserve a cup of pasta cooking water before draining. Add the drained pasta to the sauce over medium heat, tossing to coat, adding splashes of pasta water to loosen if needed. The starchy pasta water is what emulsifies the sauce and makes it cling to the pasta rather than pooling at the bottom of the bowl. Serve immediately.