1-1/2 teaspoons olive oil
1 medium onion, sliced thin and then chopped (I prefer a little bit more onion so add extra myself)
4 cups water
2 tablespoons tomato paste
2 teaspoons corn syrup
1 teaspoon corn starch (I also add a pinch or two more of this to speed the thickening process)
1/2 teaspoon salt
1/4 teaspoon crushed red pepper flakes (or less if you like it less spicy)
1/4 cup vinegar
Heat the oil in a large saucepan over medium heat. Saute sliced onion in the oil for 5 minutes, until onions are soft, but not brown. Add water, tomato paste, corn syrup, cornstarch, salt and red pepper flakes, and stir. Bring mixture to a boil, then reduce heat and simmer for 45 minutes. Add vinegar. Continue to simmer for an additional 30 to 45 minutes or until most of the liquid has reduced and the sauce is thick.
Makes about 1 cup.