Place the coriander, peppercorns, and star anise in a 1 qt saucepan and toast over medium heat, stirring often, until dark and very fragrant, 2-3 minutes.
Add the sugar and chilies and cook until melted and lightly carmelized, about 2 minutes.
Carefully and gradually add the water, and bring it to a boil over high heat.
Stir until the caramel has dissolved.
Remove from heat.
Place the rice vinegar, lime juice, lime leaves, ginger, sesame oil, and fish sauce in a bowl, and whisk to combine.
Pour the sugar syrup into the bowl, stir to combine and cover.Leave at room temperature at least 12 hours, preferably overnight.
Then strain and discard the solids.Transfer the sauce to a continer, cover and refrigerate up to 2 weeks.