2 teaspoons sesame oil
6 scallions, white part finely sliced, green part chopped into 1-inch pieces
3 cloves garlic, minced
1 tablespoon minced ginger
5 small dried chiles (optional)
¼ cup vegetable broth
¼ cup soy sauce
3 tablespoons rice vinegar
2 tablespoons mirin
3 tablespoons sugar
1 tablespoon cornstarch
Sesame seeds, for garnish (optional)
In a medium pot, heat the sesame oil over medium heat. Add the finely-chopped white scallions, garlic, ginger and chiles, and cook until fragrant, 1 to 2 minutes.
Add the broth, soy sauce, rice vinegar and mirin, and bring to a simmer over medium heat. Simmer for 5 minutes.
In a small bowl, whisk the sugar and cornstarch to combine. Pour about ¼ cup of the hot sauce over the mixture, whisking constantly until the mixture is smooth and lump free. Return the mixture to the pot and bring to a simmer. Stir in the large pieces of green scallion.
Cook, stirring occasionally, until the mixture thickens and has good flavor, 7 to 9 minutes more.