Add the frozen banana chunks, black sesame paste, milk, yogurt, honey, and a pinch of salt to the blender jar.
Blend on high for 45 to 60 seconds, stopping once to scrape down the sides, until the mixture turns silky and pale gray-purple with no visible sesame flecks.
Check the consistency. If it's too thick to pour, add 2 to 3 more tablespoons of milk and blend again for 10 seconds.
Taste and adjust. Add more honey if the banana wasn't very ripe, or a touch more salt to balance the sweetness.
Pour into two glasses and sprinkle black sesame seeds on top if you want extra texture.
Serve right away while cold. The smoothie separates slightly if it sits longer than 15 minutes.