01 - Bring a large pot of salted water to a boil. Cook the pasta according to package directions until al dente. Drain, reserving ½ cup of pasta water.
02 - Heat olive oil in a large skillet over medium heat. Add chopped onion and sauté for 3–4 minutes until translucent. Stir in minced garlic and cook for 1 minute until fragrant.
03 - Add tomato paste and cook for 1 minute while stirring constantly. Pour in crushed tomatoes, sugar, red pepper flakes if using, salt, and black pepper. Simmer uncovered for 10 minutes, stirring occasionally.
04 - Reduce heat to low and stir in heavy cream. Simmer for 2 minutes until the sauce is creamy and heated through.
05 - Add drained pasta to the skillet and toss to coat evenly. Add reserved pasta water as needed to loosen the sauce for desired consistency.
06 - Remove from heat. Stir in most of the torn fresh basil and grated Parmesan cheese.
07 - Plate immediately, garnishing with remaining basil leaves and additional Parmesan cheese.