This sweet onion sauce is made with caramelized onions rather than dehydrated onions or onion powder. It is perfect for anyone who is looking for a sweet onion sauce that gives Subway's sweet onion sauce a run for its money.
Add 2 tbsp of the vegetable oil to a medium sized pot then heat the pot over medium heat. Add the onions and sprinkle the salt over the top of the onions. Cook the onions for 25 - 30 minutes or until the onions reach a medium brown color. Stir the onions occasionally. Add small amounts of water as necessary to deglaze the pan.
Mix the cornstarch with equal parts cold water.
Add all of the remaining ingredients to the pot with the onions. Wait to add the cornstarch until the water and vinegar have already been added to the pot.
Cook the sweet onion sauce over medium low to medium heat until the sauce starts to thicken.