For roasted sesame sauce, preheat oven to 180C. Roast sesame seeds on an oven tray, stirring a couple of times, until golden brown (6-10 minutes). Finely grind sesame seeds and sugar with a mortar and pestle or, for a finer sauce, grind in a high-speed blender. Add remaining ingredients and whisk to combine.
Increase oven to 250C. Blanch broccoli until just tender, but not soft (1½-2 minutes; see cook’s notes p177). Refresh in iced water, drain and pat dry with paper towels. Oil and season broccoli with salt all over. Place in a roasting pan lined with baking paper and roast until it starts to caramelise (12-18 minutes).
Pour sesame dressing onto plates and top with roasted broccoli, scatter with bonito-flavoured sesame seeds and serve.
Note Bonito-flavoured sesame seeds are available from goodgrubhub.com.