This is the classic sauce to top a NYC “dirty-water dog” – slightly sweet and sour. Makes about 1 cup relish.
2 tablespoons cooking oil
1 large yellow onion, chopped
3 cups water
3 tablespoons tomato paste
1 tablespoon corn syrup
½ teaspoon salt
¼ teaspoon crushed red pepper flakes
¼ cup red wine vinegar
1. Heat the oil in a large saucepan over medium heat, and add the onions, cooking for about 5 minutes until softened and translucent but not brown.
2. Stir in the remaining ingredients except the vinegar, and bring the mixture to a boil. Lower the heat and simmer gently for 30–40 minutes, until softened and reduced.
3. Add the vinegar, and cook for an additional 30–40 minutes, until the onions are completely tender and the sauce is thick.