Heat the olive oil in a large, high-sided sauté pan over medium heat until shimmering.
Add the onion and sauté for 3–4 minutes, until softened and translucent.
Add the garlic and red pepper flakes, if using, and cook for 30 seconds to 1 minute, until fragrant.
Add the crushed tomatoes, kosher salt, and black pepper. Bring to a simmer and cook uncovered for 10 minutes, stirring occasionally.
Reduce the sauce to low heat and stir in the heavy cream. Taste and adjust the seasoning.
Meanwhile, cook the pasta in a large pot of salted boiling water until al dente according to the package instructions.
Drain the pasta and add it to the sauce. Toss gently until evenly coated.
Add the chopped basil and toss once more. Add a small amount of reserved pasta water if the sauce needs loosening.
Serve immediately with grated Parmesan cheese.
Storage: Refrigerate leftovers in an airtight container for up to 3 days.
Reheating: Reheat gently on the stovetop or in the microwave. Add a small splash of water or broth if needed to loosen the sauce.
