Boil the pasta: Bring a large pot of salted water to a rolling boil. Add the pasta and cook until just shy of al dente.
Reserve 1 cup of pasta water, then drain.
Warm the oil: While the pasta cooks, heat olive oil in a wide skillet over medium heat. Add the sliced garlic and red pepper flakes. Cook 60–90 seconds until the garlic is fragrant and just turning golden—don’t let it brown.
Build the sauce: Pour in the tomatoes.
If using whole tomatoes, crush them with a spoon. Season with a generous pinch of salt and a few grinds of pepper. Add the sugar if your tomatoes are very acidic.
Simmer briefly: Let the sauce bubble gently for 8–10 minutes, stirring now and then.
You want a lightly thickened, glossy sauce that still tastes fresh.
Finish with butter (optional): Stir in the butter for a rounder, silkier finish. Taste and adjust seasoning.
Marry pasta and sauce: Add the drained pasta to the skillet. Toss over medium heat, adding splashes of reserved pasta water until the sauce clings to the pasta and looks shiny.
This usually takes 1–3 minutes.
Add herbs and cheese: Turn off the heat. Fold in torn basil or parsley. Plate and top with grated Parmesan.
Serve hot: Finish with a drizzle of good olive oil, extra pepper, and more cheese if you like.