Step 1
Make the tomato sauce: In a medium saucepan, heat the oil over medium heat. Add the onion, garlic and crushed red pepper flakes, and cook, stirring frequently, until softened, 10 to 12 minutes. Add the tomatoes, basil, vinegar, sugar and Parmesan rind, and bring to a simmer. Lower the heat to medium low and cook, stirring occasionally, until slightly thickened, about 25 minutes. Discard the Parmesan rind and, using an immersion blender, blend the sauce until slightly smooth while retaining some texture. Season with salt and pepper to taste.