Subway Sweet Onion sauce

1. In a medium saucepan, combine sugar, red wine vinegar, white vinegar, grated onion, sesame oil, Dijon mustard, mustard powder, onion powder, garlic powder, paprika, celery seed, poppy seeds, salt, and pepper.
2. Whisk until smooth.
3. In a small bowl, mix cornstarch with a little water until smooth.
4. Add cornstarch mixture to saucepan and whisk until well combined.
5. Bring mixture to a boil over medium heat, stirring constantly.
6. Reduce heat to low and simmer for 5 minutes, or until sauce has thickened.
7. Remove from heat and let cool.