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