Begin by bringing a large pot of salted water to a boil. Once boiling, add the angel hair pasta and cook according to package instructions until al dente. Drain the pasta in a colander and set aside.
In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté for about 3-4 minutes until the onions become translucent. Next, add the minced garlic and cook for an additional minute, being careful not to burn it.
Stir in the dried basil and crushed red pepper flakes. Allow the spices to bloom for about 30 seconds, releasing their fragrant oils.
Pour in the jar of spaghetti sauce, stirring well to combine with the onion and garlic mixture. Let it simmer for about 5 minutes, allowing the flavors to meld.
Reduce the heat to low and stir in the heavy cream. Allow the sauce to simmer for an additional 3-4 minutes until it thickens slightly. Add the black pepper and salt, adjusting to your taste.
Finally, add the cooked angel hair pasta to the sauce, tossing gently to coat. Serve immediately, garnished with fresh basil or grated Parmesan cheese if desired.