Heat olive oil in a large sauté pan or medium saucepan over medium heat.
Add the onion and a pinch of salt and cook, stirring frequently, until softened, about 5 minutes.
Add the garlic and crushed red pepper flakes and cook, stirring, for 1 minute more.
Add the crushed tomatoes and sugar and stir to combine. Bring to a bubble, then reduce the heat and allow to simmer for 15-30 minutes.
While the sauce is simmering, bring a large pot of water to a boil. Cook and drain pasta according to package direction, reserving ½ cup pasta water before draining.
Remove the sauce from the heat, season with salt and pepper to taste, and add the basil. Toss the sauce with the spaghetti and serve topped with additional red pepper flakes, basil, and parmesan cheese if desired.
Tips for customizing
Use whatever pasta shape you have on hand such as penne or rigatoni
Substitute the crushed tomatoes with diced tomatoes
Adjust the heat in this dish by adding more or less crushed red pepper flakes
Serve with a salad or top with grilled veggies for extra nutrients