2Heat ¼ cup extra-virgin olive oil in a large skillet over medium-low. Cook 1 medium onion, finely chopped, stirring occasionally, until translucent and softened, 10–12 minutes. Add 4 garlic cloves, finely chopped, and cook, stirring often, until fragrant and softened, about 3 minutes. Add a pinch of crushed red pepper flakes; cook, stirring, 1 minute.
3Increase heat to medium and add puréed tomatoes to skillet; season lightly with kosher salt. Bring to a simmer and cook, stirring occasionally, until sauce is slightly thickened and flavors have melded, 20–25 minutes. Remove from heat and stir in 3 large basil sprigs.
