1) Heat the oil in a medium saucepan over medium-high heat. Add the onion and cook, stirring, until lightly browned, about 4 minutes. Add the garlic and crushed pepper and cook, stirring frequently, until fragrant, about 45 seconds. Add the tomato paste and cook, stirring, until lightly browned, about 1 minute more.
2) Add the tomatoes, vinegar, sugar, and salt and bring to a boil. Lower the heat, and simmer, uncovered, stirring occasionally, until deep red in color and reduced to about 950ml, about 25 minutes. Season with pepper to taste. Use now, or store, covered in the refrigerator for up to 3 days or freeze for up to 1 month.