Boil water: Fill a large pot with water, add a generous pinch of salt, and bring to a rolling boil.

Cook pasta: Add spaghetti to the boiling water and cook according to package instructions until al dente. Reserve 1 cup of pasta water before draining.

Prepare sauce base: Finely chop onion and garlic. Heat olive oil in a pan over medium heat, then sauté onion until translucent. Add garlic and cook for 1 minute until fragrant.

Make tomato sauce: Add canned tomatoes to the pan, breaking them up with a spoon. Season with salt, pepper, and sugar. Simmer for 15 minutes, stirring occasionally.

Combine pasta and sauce: Add drained pasta to the sauce, tossing to coat. Add reserved pasta water as needed to loosen the sauce.

Finish and serve: Tear fresh basil leaves and stir into the pasta. Serve hot with grated Parmesan cheese on top.