Bring a large pot of salted water to boil. Add pasta and cook for 6 minutes or until just before al dente (i.e. slightly undercooked, very firm to touch). The pasta will be cooked more in the pasta sauce.

Meanwhile, heat olive oil in large pan over medium high heat. Add onion and garlic and sauté for 3 minutes.

Add remaining ingredients. Bring to rapid simmer, stirring occasionally. Adjust seasoning with salt and pepper. If the sauce seems too thick, add a splash of the pasta cooking water.

Use tongs and transfer the pasta straight from the pot of boiling water into the pan with the ragu sauce. Add 1/2 cup of pasta cooking water and gently toss the pasta in the sauce for 1 to 2 minutes. The pasta is ready when the spaghetti is al dente (cooked but slightly firm to touch) and the sauce has thickened and is tossed through the pasta.

Serve immediately, sprinkled with freshly grated parmesan cheese and parsley if desired.