Start your pasta water and cook until just under-cooked.
Meanwhile, heat a large saucepan coated in low- fat cooking spray and saute the onion until soft (about 5 minutes).
Add the garlic and cook for about a minute more (being careful not to let it get too dark).
Add the tomatoes, season with salt and pepper and cook, uncovered, over medium heat for about 10 minutes.
Taste the sauce and if you need to cut down on acidity, add a pinch of sugar.
Add the half and half and Parmesan cheese. Season to taste and cook on low heat another few minutes.
Drain the pasta (reserving some of the pasta water)and add it to the pan with the sauce. Coat the pasta and add a little pasta sauce to loosen if need be.
Serve hot once the pasta is desired softness.
Video
Notes
Cook the spaghetti until just undercooked and finish cooking in the sauce.
Don't add oil to your pasta water. This will cause the sauce to slip off the pasta instead of coating it.
Taste as you season. Some parmesan cheeses are quite salty so you may want to wait to season with salt until after you've added the cheese. Then taste, add the salt and taste again.