Boil a pot of water for the pasta.
Break the sausage meat out of the casings. Heat a large stock pot or a dutch oven over medium high heat, and add the olive oil. Add the sausage, breaking up as you cook it almost all of the way through. When almost done, add the onion to the pan, continuing to break up the sausage meat. The idea is to give it a similar consistency to ground beef almost, so the sausage is distributed throughout the sauce at the end.
When the sausage is fully cooked, and onions translucent, add the garlic, red pepper flakes, salt and pepper, and cook for one minute, being careful not to burn the garlic. Add the jar of sauce, and simmer over low heat while the pasta cooks.
Cook the pasta according to package directions, al dente. Drain when finished, reserving a cup of the cooking water in case you want to thin the sauce. Add the cooked pasta directly to the sauce in the large pan, stirring to combine. Thin to your liking with the starchy pasta cooking liquid.
Turn off the heat, and add the parmesan, basil, and salt and pepper again if needed. Likely you won't need much extra seasoning, with the sauce and sausage. Serve in large shallow bowls with extra parm and freshly torn basil. I like a little extra red pepper flakes on mine.