Salt and boil the water. Fill a large pot with water and bring it to a rolling boil.
Add a generous handful of salt. It should taste like the sea for well-seasoned pasta.
Start the aromatics. In a large skillet or sauté pan, warm the olive oil over medium heat. Add the onion with a pinch of salt and cook 3–4 minutes until soft and translucent.
Add garlic and heat. Stir in the garlic and red pepper flakes.
Cook 30–60 seconds, just until fragrant. Don’t let the garlic brown.
Build the sauce. Pour in the crushed tomatoes. Add 1/2 teaspoon salt, a few grinds of pepper, and the sugar if your tomatoes taste sharp.
Simmer on medium-low for 8–10 minutes, stirring occasionally.
Cook the pasta. Drop the pasta into the boiling water. Cook until just shy of al dente, 1–2 minutes less than the package suggests. Reserve 1/2 cup of the starchy pasta water before draining.
Enrich the sauce. Stir the cream and butter into the tomato sauce. Let it gently bubble for 2 minutes to marry the flavors.
Taste and adjust salt and pepper.
Marry pasta and sauce. Add the drained pasta straight to the pan with the sauce. Sprinkle in the Parmesan and a splash of reserved pasta water. Toss over medium heat for 1–2 minutes until glossy and well-coated.
Add more pasta water as needed to reach a silky texture.
Finish fresh. Turn off the heat and fold in the basil. Taste again and adjust seasoning. Serve immediately with extra Parmesan on top.