01 - Bring a large pot of salted water to a boil. Cook the pasta according to package directions until al dente. Reserve 1/2 cup of pasta water, then drain the pasta.
02 - Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook for 4 to 5 minutes until softened.
03 - Stir in the minced garlic and cook for 1 minute until fragrant.
04 - Pour in crushed tomatoes, sugar, salt, black pepper, and red pepper flakes if using. Simmer uncovered for 10 minutes, stirring occasionally.
05 - Reduce heat to low and stir in heavy cream. Simmer for 2 to 3 minutes until the sauce becomes creamy.
06 - Add the drained pasta and Parmesan cheese to the sauce. Toss thoroughly, adding reserved pasta water as needed to achieve a silky texture.
07 - Remove from heat. Stir in most of the torn basil leaves, reserving some for garnish. Serve immediately, topped with extra Parmesan, a drizzle of olive oil, and remaining basil.