In a small saucepan, combine olive oil, minced garlic, hot pepper flakes, and packed basil leaves. Heat over medium-low until the mixture sizzles, cooking for about 45 seconds to 2 minutes, until the basil wilts. Remove from heat and set aside.

In a Dutch oven, melt the butter over medium heat. Place the halved onion cut side down and sauté for 4-5 minutes until lightly browned.

Add the San Marzano tomatoes to the pot, using a potato masher to break them into chunky pieces. Bring the mixture to a gentle simmer, reducing the heat to medium-low and letting it simmer for 20-25 minutes.

While the sauce simmers, cook the spaghetti according to the package directions but remove it two minutes early.

Once your sauce has simmered, pour the cooled oil mixture into a food processor and chop until finely integrated. Add this aromatic oil to the tomatoes and simmer for an additional five minutes.

Remove the onion from the sauce, taste, and adjust seasoning with salt and pepper. Add the partially cooked spaghetti to the pot, cooking for an extra two minutes until the pasta reaches al dente perfection.

Transfer the Spaghetti Pomodoro to a serving platter, sprinkle with grated parmesan cheese, garnish with extra basil leaves, and drizzle with olive oil. Enjoy!