Put all ingredients except for the mixed seeds and powdered gelatin into a pot. Whisk well as you heat and dissolve over medium heat. (Do not let it boil!)
Turn the heat off when it's slightly bubbly. Add powdered gelatin and dissolve fully. Set aside to cool down, then cool the the pot in a bowl of ice-cold water as you stir thoroughly.
When the mixture has thickened, pour into cups and chill in fridge to harden (it only takes 50 minutes if you put in freezer). Top with mixed seeds if you'd like, and serve.
The sesame paste and milk will separate into two layers if you don't cool it down in ice-cold water. This is also delicious since the sesame part tastes really rich, almost like kinako (roasted soybean powder) sauce!
Story Behind this Recipe
I had leftover sesame paste, so I dissolved that into milk and hardened it with gelatin to make pudding.
The reason why you chill the bottom of the pot in ice-cold water after the gelatin is dissolved is to prevent the sesame paste and milk from separating. It also hardens much faster if you cool it down and stir to thicken before pouring it into a container. If you don't cool the mixture down thoroughly, it will form two layers. It's also tasty that way.