Add 2 tbsp white sesame seeds to a dry frying pan and gently toast over a medium heat until fragrant and slightly golden. Shake the pan regularly and remove from the heat as soon as they're done to prevent burning.
Pour the hot sesame seeds into a mortar while they are still warm. Grind with a pestle until they're half paste, half powder.
In a separate bowl, mix 1 tsp unseasoned rice vinegar (komezu), 1 ½ tsp sugar, and 1 tsp Japanese soy sauce (koikuchi shoyu) until the sugar has dissolved. If you're using ⅛ tsp dashi granules, add them here too.
Add the ground sesame to the bowl along with 2 tbsp Japanese mayonnaise. Whisk until smooth and creamy.
Drizzle in 1 tsp toasted sesame oil and whisk until combined. Use straight away, or chill in the fridge for 15-30 minutes. Enjoy!
Large batch (16 portions)
Toast 140 g white sesame seeds in a large dry pan until golden and fragrant, then pour into a food processor and blitz until they become half paste half powder.
In a small bowl, whisk 40 ml unseasoned rice vinegar (komezu), 40 ml Japanese soy sauce (koikuchi shoyu), 4 tbsp sugar and 1 tsp dashi granules (optional). Whisk until all the granules have dissolved, pour the mixture into the food processor. Add 230 g Japanese mayonnaise and 40 ml toasted sesame oil. Pulse until smooth, creamy and well combined.
Enjoy!
Notes
Stop toasting at the aroma, not the color: Sesame burns in seconds, and once it is scorched the bitterness barely rinses out. Pull it off the heat the moment it smells nutty and a few seeds pop, before real color arrives.Dissolve the sugar into the liquids first: Stir the sugar into the vinegar and soy sauce until it fully melts before it meets the sesame. Dropped onto the oily ground sesame it stays as grit and the dressing turns sandy.Grind the sesame while it is still warm: Warm seeds give up their oil as you grind, and that fresh oil is what gives it body. Stop at a half-paste, just before the oil weeps out.No suribachi needed: A suribachi gives the smoothest paste, but a clean coffee or spice grinder, a small blender, or a zip-top bag and a rolling pin all break the seeds down too. Aim for a texture that clings together, not a loose dry powder.Taste and steer it before it dresses the greens: Too sweet, a splash of vinegar pulls it back. Too sharp, a pinch of sugar rounds it out. Aim a hair bolder, since the leaves soften every note.Go easy on the optional dashi: A pinch adds a savory backbone, but it also nudges the salt up, so add it lightly and taste before adding more.