You only need five ingredients (not including salt!) to make our ultimate red sauce.
Heat a straight-sided skillet over medium. Swirl in oil; add onion and 1 teaspoon salt. Cook, stirring occasionally, until onion is soft and translucent, 7 to 9 minutes. Stir in garlic and red-pepper flakes; cook 30 seconds. Add tomatoes to skillet; bring to a boil. Reduce heat and simmer, stirring occasionally, until reduced and thickened slightly, about 20 minutes.
For the purest fresh-from-the-vine flavor, we like Muir Glen Organic whole peeled tomatoes, available at most grocery stores.