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