Heat a small pan over medium heat and add sesame seeds in a single layer. Stir constantly for 3-5 minutes until seeds turn golden brown and smell nutty. Watch closely to avoid burning.
¼ cup toasted sesame seeds
Transfer toasted seeds to a mortar and pestle or spice grinder while still warm. Grind for 15-30 seconds to a coarse powder with some visible pieces. Avoid grinding into a paste.
¼ cup toasted sesame seeds
Whisk ground sesame seeds, soy sauce, rice vinegar, and mirin in a bowl until combined. The mixture may look grainy and separated at this stage.
¼ cup toasted sesame seeds, 2 tablespoons soy sauce, 1 tablespoon rice vinegar, 1 tablespoon mirin
Add sesame oil in a thin stream while whisking vigorously for 1-2 minutes until the dressing turns glossy, creamy, and no oil pools on the surface.
2 tablespoons toasted sesame oil
Whisk in sugar in ½ teaspoon increments, tasting after each addition until balanced. Add dashi or water 1 tablespoon at a time if the dressing is too thick for drizzling. Transfer to an airtight jar and chill for 20-30 minutes before serving.
1 teaspoon sugar, 2 tablespoons dashi or water