01 - Bring a large pot of salted water to a boil. Cook pasta until al dente according to package instructions. Reserve ½ cup pasta water, then drain pasta.
02 - Heat olive oil in a large skillet over medium heat. Sauté onion until soft and translucent, about 4 minutes. Add garlic and cook 1 minute until fragrant.
03 - Add crushed tomatoes to the skillet. Stir in sugar if using, season with salt and pepper. Simmer for 10 minutes, stirring occasionally.
04 - Reduce heat to low. Stir in heavy cream and let sauce gently bubble for 2 minutes until creamy.
05 - Add drained pasta to skillet and toss to coat. Add reserved pasta water as needed to achieve a silky sauce consistency.
06 - Stir in butter, Parmesan, and most of the basil leaves, reserving some for garnish. Cook for 1 additional minute.
07 - Plate immediately and garnish with extra Parmesan and fresh basil.