the recipe from the link above as well
1 1/2 teaspoons olive oil
1 medium onion, sliced thin and chopped
4 cups water
2 tablespoons tomato paste
2 teaspoons corn syrup
1 teaspoon cornstarch
1/2 teaspoon salt
1/4 teaspoon crushed red pepper flakes
1/4 cup vinegar
1. Heat the oil in a large saucepan over medium heat.
2. Sauté sliced onion in the oil for 5 minutes, until onions are
soft but not brown.
3. Add water, tomato paste, corn syrup, cornstarch, salt, and red
pepper flakes, and stir.
4. 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
Makes about 1 cup.
The author also suggests doubling the recipe due to the time it takes to create the sauce. I'd say to double it cause it sounds great and I can't imagine that one cup would be enough.