Now add the puréed tomatoes to the pan and stir over medium-low heat for about 15 minutes.
Now add 1/4 teaspoon of sugar, 1/4 teaspoon kosher salt, and 5 chopped basil leaves.
Cook for an additional 5 minutes and serve over hot buttered pasta.
Notes
Don't rush the onions and garlic- Cooking these two first is important because they need time to soften and release their aromatic flavors.
Pulse the tomatoes just enough- You want this sauce to end up being thick with small pieces of tomato. Under-blending will leave it too chunky. Over-blending will result in a runnier sauce.
Don't skip the sugar- This adds a little sweetness that balances out the salt and acidity in the recipe.