In a pan saute, garlic and onion, make sure you do not burn it, they turn bitter. Prior to the garlic and onion being translucent, toss in the chopped up tomato. Stir to blend flavors.
Add in the tomato puree and basil. The onion should be enough to keep it from being to acidic so you should not need sugar. If you use anything use a pinch of baking soda it cuts the acid. Salt and pepper to taste. Also the chopped up tomato gives it a nice consistency.
For variations, I add red crushed pepper to make it spicy, you can add 1/4 cup of cream to make it a ight pink sauce, with the cream you can add vodka, red crushed pepper to make it al la vaodka, or you can use a 1/2 cup of red wine to make it more of a northern sauce. This is a great started sauce that you can change to suit your needs. I often have two little containers in the freezer stored so I can make soemthing quick out of it, including adding some meat to make a simple meat sauce.