Step 1

Heat the oil in a large saucepan over medium heat. Sauté the sliced onions in oil for 5 minutes, until the onions are soft but not brown.

Step 2

Add 3 cups of water, corn syrup, corn starch, tomato paste, salt, and pepper flakes and stir. Bring to a boil, then lower the heat and simmer for 45 minutes.

Step 3

Add vinegar. Continue to simmer an additional 30-45 minutes or until most of the liquid has reduced and the onionsauce is thick.