In 3-quart nonreactive saucepan, heat 2 tablespoons oil over medium heat.
Add onion; cook 4 to 6 minutes, stirring occasionally, until translucent.
Stir in parsley and garlic; cook about 30 seconds or until fragrant.
Stir in tomatoes, basil stem and salt.
Simmer uncovered 20 to 30 minutes, stirring frequently, until thickened.
(If sauce tastes too acidic, add pinch of baking soda and cook 5 minutes longer.
If sauce needs touch of sweetness, add pinch of sugar and cook 5 minutes longer.)
Remove basil stem before serving.